I dunno, this whole fiddling with shops thing seems like it would really hurt the procedural/decision-making part of a dungeon crawl and be needlessly fiddly. I don't know if it's just that I've left a couple of the rougher viciouses alone so far but I think being able to *rely* on the shops being useful will cut a huge amount of unpredictability (which is in moderation a good thing) from runs. A small blacklist as a prep isn't a terrible idea (and would give you somewhere to look at what items you've unlocked), though I think it makes it only more likely I would keep ignoring any items I'm ignoring at the moment. Re total buyout runs - now we've got the gold-sink items and a lower starting point they're a lot rarer (I tend to have elite items prepped, so very rare for me), and even then the spare gold can go to TT piety... I think it's fair to say that almost invariably a total buyout run will give you some sort of advantage and it's a bit silly to expect every run of that kind to offer roughly equal value - heavy gold runs are meant to be a bit risk-dependent on what you find.
I dunno, finding out what's in the shops without any foreknowledge or ability to directly affect that is a nice part of the procedural bit of DD... I think this'd just turn shopping into another element of the game to be prepared beforehand whereas now it works quite nicely as a random element. The only occasion in which you might absolutely *need* a particular item or type of item to show (in addition to a locker, potions and a blacksmith prep) is using tricky classes in viciouses.