For what its worth I think absolutely.
7.3.x is well field tested now, it means you can re-write procedures without the annoying 16 param limit in mind, and for a non point number release there is nothing wrong with the removal of previous database version compatability.
If people (like me) have custom packages, they can run production sites on 4.6.3 and migrate to a development system running 5.0/7.3.x
I think prodding people forward like this is good for everyone, its not like commerical software with a 'we will no longer support you if you do not upgrade' clause, so there is no gun to anyones head.
Roger.