what model are you printing? if it has the cad for adjusting tolerances, print a few to find the loosest one that will hold to some moderately aggressive typing and you should be fine. If its too tight it can be hard to get them off depending on how beefy the stem hole surroundings are. I only really print abs so I don’t know about pla specific but I did a set for a friend in sparkle orange and months in all I hear about them is how much he loves them. I thought they looked kinda mediocre to be honest though, I could have tuned printer more before committing to the whole set. Bambu you probably don’t have to worry about that from what I’ve heard though.

edit: I somehow missed that you mentioned the model right at the beginning…

Honestly it doesn’t seem like there’s a lot of risk with giving it a try. If it doesn’t work out, you can always buy regular commercially-available keycaps later.

You mentioned the potential of stems breaking off in the switch. I kinda doubt that’s terribly likely. (If they break off, I’d think the chunks that broke off would be big enough that they wouldn’t end up in the mechanism of the switch and could just be shaken out or retrieved with needle-nose tweezers.) That’s just speculation on my part, but I have plans to print myself some self-designed keycaps (and a self-designed keyboard base, in fact) at some point out of PLA and I’m not terribly concerned about that potential issue. I also don’t really mind buying more keycaps later if I need to, though.

3D-printed keycaps can also be replaced easily. If you’re concerned about them breaking, you might want to print some extras up front so you don’t have to wait for a print to finish before you can use your keyboard again. (And so you don’t have to try to use it with one keycap missing. Lol.)

I have a couple of escape keys that I use, but they are too hard and the feeling is not uniform enough to use for other keys really. I wouldn’t trust them for regular alphabet at all. Especially for keys that have more angle to them they end up having a lot more topography to them.

The stems also can’t take as much abuse unless you went ahead and filled the whole key in.

I have no experience with printing key caps but do have experience with FDM and MSLA printing. I don’t think PLA is probably your best choice, but PLA+ might be. TPU would be too soft (tough) and standard PLA might be to brittle (hard). Physics sounds weird irl.

I have some Cherry XDA profile caps that I printed in Protopasta Matte PLA. They work surprisingly well. I’d say go for it.