It's not entirely clear to me that it's desirable, just in terms of user expectations, for links in man pages to go to Info pages.
Multiple installed hierarchies are a different problem, aside from anything about man pages. Info has always had the concept of one merged dir file for the whole system and INFOPATH determines precedence of what is found. Although deficient in theory, it seems to suffice in practice. I don't recall lots of bug reports about it. Especially now that it's become much clearer what Info file gets found and how to visit other ones. k
