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 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.