I think CA handled that really well with Krobus. If you have him as a roommate, a chest takes the place of his usual spot in the sewers, and you can buy from it as if Krobus had actually been standing there. Maybe something similar to that could be done in the future for other NPCs with shops?
Or maybe something similar to what happens now when they go to Ginger Island - they could leave a note saying "put the money in this box" and then you just buy as usual.
But yeah, I assume that's the reason Gus, Clint, Marnie, and Willy were not originally marriage candidates. Especially Gus, who would have to stay at the saloon until 12 - he might not even be able to walk back to the farmhouse by 2am.
Although I guess Maru and Harvey sort of run a shop (the reception desk at the hospital). Maru's only there twice a week, so she can continue working there after marriage while still staying on the farm for the majority of days like other spouses do, as opposed to someone like Clint or Willy who would just never be on the farm during the day if they kept their normal shop hours.
Question to anyone who's married Harvey: The wiki says he's only at the clinic two days a week after marriage. Are you still able to buy energy tonics and muscle remedies from the clinic on days that aren't Tuesday or Thursday (the days Maru works there)? If so, I'd assume the same thing could be done for other shopkeepers. But obviously the clinic reception desk is a lot less vital to the game compared to all the other shops.