Personally, I already saw some incompatibilities, and following two are those who stopped for a bit my migration:

When I tried my real-life script on 5.8.0 that used to run okay with 5.6.1, I found out that it just stopped working. It appeared that :crlf layer, which is set by default on Win32, contains a bug in respect in functions tell/seek, I reported it, it's number is #15986.

Also, E.Page was used to release new version of "ptkdb" debugger that contains a hack-like addition to make ptkdb work with 5.8.0 - something seems to be broken in DB::DB debugger interface.

But anyway, I have both newer and elder perls installed on my machine, and I try them both from time to time.

Courage, the Cowardly Dog