Are there issues with sharing /home and other directories between linux distributions on the same system? What about sharing between linux and bsd?
Just curious.
Not really, no. The only hypothetical issue is configs between your programs clashing due to version differences. IME, though, that’s a rare problem except with maybe Firefox, which can be a stickler for version numbers.
I don’t know how BSD works, but linux has $XDG_ configs in homedir of user for most configuration files.
You could sidestep any conflicts by just changing your linux-systems $XDG_ -environmental variables to something like ~/.local.linux, ~/.config.linux and so on.
Ultimately almost any path under $HOME can ba changed with corresponding environmental variable in linux - so you can split directories if necessary.