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.
You’re right - my main concern is the stem breaking in the switch. The choc switches are a little difficult if the little keycaps stems break in them.😕