Pardon me but AFAIK all JDKs are backwards-compatible. Unless you're doing some weird sh*t which exploits JRE bugs (oh, sorry.. features). But that just makes you a bad dev as you tie yourself to the implementation rather than specification. The _unsafe_ part being removed is not bckw_compat, I give you that. But if you're tied to this hole you're doomed to become legacy code maintainer as it's not coming back.

Just upgrade to OpenJDK_v(N+1) whenever it's out. Get rid of Karaf, Liferay or whatever is holding you back. Don't become a legacy app developer.