Would we be able to buy them from the merit vendors? 
Well, not really for or against this. It would be a nice perk, but players have different ways to get merits.
And I would like it a bit simpler as a straight drop, like they do not with the recipe drops from bosses and up or like with GMs but very rare/random. A recipe would need salvage and has to be crafted, which may cost some depending on the salvage.
I think it would be fun, moreso if the recipes rewarded a variable amount of merits when crafted. Though I haven't seen any purple or respec recipes in forever so I'd probably never see one.
total kick to the gut
This is like having Ra's Al Ghul show up at your birthday party.
PSSHHT!
I've NEVER seen a purp or respec recipe... been too much of a casual gamer in the past few months... heck, I have like 20 merits... total... accross several toons!
I don't see a reason why NOT to have this type of recipe in game... might end up in WW/BM for me to buy...
Just came to mind, and I thought I'd toss it out there.
How about a recipe (or series of, say, 3) that would reward some amount of merits (say, 5, 8, 10, or 5, 10, 15) when used?
Yes, I know some folks would see nice streaks of these, others wouldn't, but if they dropped about as often as some of the others, I wouldn't think they'd be exceptionally common. (F'rinstance, I haven't seen a respec recipe in months, I get perhaps a power analyzer a month, costume bits every few weeks - the same sort of drop rate should make these pretty decent.)
Yeah, I know, "Farmers." *shrug* I don't honestly believe they'll have that huge of an impact on these - they'd probably use them themselves.