I think a mixed tank works well if you avoid agresive softies and keep proper separation for LPS.
Some softies or LPS I would not keep in a mixed tank are Sinularias, hydonoporas, Kenya Tree and similar. Sarcopythons might be OK the issue is they need lots of space as they will grow fasT and large.
OK will be Xenias (keep them rounded with some shells you can remove to keep them tripped, some zooanthids and GSP if contained by rubble, shells or sand, mushrooms, ricordeas, heliophoras, open brains, caulastreas, organ pipe (Clavularia), Alveoporas, Euphylias (Frogspawn), ancoras, fotosynthetic gonioporas and such.