@Jeffro - There's no current plan to eliminate it, I simply expect it based on the way things happen... I did make a ticket to this effect, actually, but I suggest deprecating it for a version or two first.

As far as keeping up with changes... if you want to be a serious plugin developer, then I'd get involved in core development as well. Subscribe to the wp-trac mailing lists. Download the trunk SVN and run a local copy which you do an "svn up" on every so often. Give your opinion on trac every once in a while. Contribute a patch or two.

You can't be a really good WordPress developer without keeping up with and helping out with the core code as well, IMO. There's no real difference between "plugin" and "core" developers. There's just "WordPress developers".