Flasks are indeed under Elixirs, but with the coming nerf to them the market will be more limited. But for a rather hardcore guild a Master of Elixirs would certainly be nice.
Transmute Mastery isn't really for arcanite bars (a bit obsolete nowadays), more for Primal Might and rare jewels. There's definitely a market, but transmutes are once a day and I can feel the frustration building up because it will necessarily seem like extra transmutes won't proc as often as extra pots or elixirs (what I mean by that is that I brew potions 5x a day without thinking about it, and I will get extra proc every couple of days or so at worse, whereas I might do one transmute per day and I will be very "focused" on the outcome).
Re: what Redistayn is staying, major healing pots are... kind of obsolete too. But the endgame healing and mana pots are selling very well, same for quite a few elixirs (e.g. major strength).