See https://github.com/hibernate/hibernate-search-6-poc/pull/93/files/1a8c67d4002e5642fcfd782dfad0468a6b45a088..6249c1bbd63ed870e8fa0b33e50e3572de235f9b#r214029552

In particular this:

Then, the isCompatibleWith method is really too coarse-grained. At some point we will need multiple ways to determine "compatibility" between indexes, because being compatible when projecting is not the same as being compatible when defining predicates, for example. Right now we just enforce the strictest (and most limiting) definition of "being compatible".