There are, as people have noticed, a small handful of very expensive items on vendors in Legion. This isn't anything fundamentally new - the original Kirin Tor Signet Ring cost a small fortune in relative terms when it first came out in Wrath, as did the Grand Expedition Yak in Mists.
When it comes to cosmetic items and convenience perks, they vary tremendously by source, both in terms of playstyle and degree of difficulty. Some are widely-earned rewards, some were simply a matter of being around at the right time (e.g. the Onyxian Whelpling), others require tremendous skill (Gladiator mounts, Mythic raid mounts from current content), while others require a combination of persistence and luck (Time-Lost Proto Drake, Elegon's mount, etc.). Some require you to engage in PvP, others require raiding, others require extensive outdoor gameplay, or profession use. And some require a sustained and concerted effort to accumulate a ton of gold.
Besides, think of it as a favor to all the arachnophobes out there - do you really want massive spiders skittering around everywhere?
Just to be clear, I agree that the Mad Merchant isn't going to serve as a very effective gold sink. But that's because he isn't intended to be one in any meaningful sense. Gold sinks, in an MMO economic sense, are primarily things like repair costs, the Auction House tariff, and a range of useful expensive items that still fall within the price range of many guild banks and gold-rich players. In this case, a handful of very wealthy players may dump a large portion of their gold reserves into this one vendor, but that's ultimately a blip in the grand scheme of the WoW economy.
If we wanted to drain as much gold as possible out of the economy using these items, we'd be pricing them differently. If the cost 200k, I'd wager that far more than 10x as many would be sold. Inflation is a concern, but that's a battle that will be waged on many other fronts. This is just a crazy merchant. The point of the items is to be ludicrously expensive, just as the point of something like the Time-Lost Proto Drake is to be ludicrously rare (if you think about it, a multi-day respawn that shares a spawn point with a more common variant and has a zone-wide patrol is pretty insane...). Some of the vendor's details may be tweaked, and there's been very good feedback in the thread on the relative attractiveness of the different items, but the 2mil price tag for the mount is not likely to change.
I'm sorry it feels that way. This is going to be a lengthy post that will stray far afield from the topic of expensive vendor items, but there there are at least two major underlying issues here:
First off, there are multiple viewpoints on nearly any topic, as you can see in this thread. If I'd instead posted that we were going to reconsider and massively reduce the prices of the cosmetic items on this vendor, there would be other people feeling like their feedback was ignored. It's exceptionally rare that everyone wants the same thing (despite frequent framing of "no one likes X" or "we want X" when giving feedback). And even then, there is a large silent majority that does not post on forums. If there were actual unanimity regarding a certain issue, we would change our design: For example, early on in Warlords, we changed Group Finder loot from Personal back to Need/Greed until we could iterate on Personal loot further, and the community overwhelmingly told us that was a dumb idea. The change was reverted within 2 days.
Second, almost every facet of WoW is an activity that caters to a minority of the playerbase. That may sound odd at first blush, but it's true. In a sense, that's part of the magic of WoW. It is not a narrow game, but rather one that can be enjoyed in numerous different ways, by people with hugely diverse playstyles. A minority of players raid. A minority of players participate in PvP. A tiny minority touch Mythic raiding. A tiny minority of players do rated PvP. A minority of players have several max-level alts. A minority of players do pet battles, roleplay, list things for sale on the auction house, do Challenge Mode dungeons, and the list goes on. Virtually the only activity that a clear majority of players participate in is questing and level-up dungeons, but even then there's a sizeable group that views those activities as a nuisance that they have to get through in order to reach their preferred endgame.
And yet, taken together, that collection of minority groups literally IS the World of Warcraft.
Perceptions of feedback are further complicated by the fact that, due to the cooperative nature of the game, players tend to make connections with others who favor a similar playstyle. I'm generalizing a bit here, and there are certainly exceptions, but I'd guess that a typical Gladiator-level player probably doesn't have a WoW social group that consists of people who mostly solo-level alts and explore the world. And most small friends-and-family guilds don't spend a lot of time talking to competitive Mythic raiders. So when there's a change, or a feature, that is aimed at a portion of the game that isn't your personal playstyle, it's easy and in fact natural to have the sense that "everyone" dislikes it.
If we decided to focus on a specific playstyle and elevate that portion of audience above the rest, then we could certainly visibly and consistently address clear feedback from that group, but WoW would become a far smaller game in the process.
Another major consequence of this structure is that if we have some special reward (be it a unique mount, a powerful item, a title, etc.) and we choose to associate it with a particular playstyle, almost by definition a majority of player feedback will be against that decision. For example, if an awesome mount comes exclusively from PvP, the majority of players who don't participate in PvP yet desire the mount would prefer that it were otherwise. If our goal were to please a majority, we would likely have to make a version of that mount also available through raiding, and one also available through outdoor questing and reputation, at the very least. But doing that would dilute the reward itself. Ultimately, the approach we take is usually to tailor different content and rewards that can feel special to different groups, rather than trying to come up with a lowest common denominator that isn't special to anyone.
In closing, I know it often can seem like we don't listen. We are - just to many, many different voices. And it may be that a given change, feature, or reward is simply aimed at a different portion of the playerbase. Or we could be wrong and we haven't realized it yet. So please, keep talking.
The only reason is that it's difficult to make absolute "never"-type statements with confidence. We have no plans to offer a recolor or highly-similar version of the Widow, as we agree that it would undermine the value of the mount (highly debatable though it may be) if there were easily-obtainable variants.
But in the distant future? Who knows. Maybe some day we make a spider expansion, all about spiders, complete with a playable arachnid race (this is where I alienate all the arachnophobes who were grateful for my first post in this thread), and there are spider mounts everywhere. So I can't say "never."
But in general, we feel that we've diluted the impact of some of our mounts by offering numerous variants of the same base creature. It's appropriate for some creatures, especially where it feels like a prominent part of the natural fauna of a new continent (e.g. all the various Proto-Drakes in Wrath, or Cloud Serpents in Mists), but when something is unusual we should try to keep it that way. A mount like the Ratstallion should also remain unique for the foreseeable future.