my two cents:

There's no way to enforce referencial integrity (easily) between databases; you can try putting contraints using user defined functions, but that does nto guarantee anything,a s the databases can be restored/dropped seperately. that's just introducing a new level of complexity that you don't really need.

commands involving linked server are slow. If you select/update/delete data, the linked server table is copied over to tempdb, the joins are formed,a nd then the select/update/delete is finally executed.

that whole copying of the data, especially if big tables are involved, is a performance hit you can avoid by not breaking up the database.