It would ease migrating to 3.0.x a great deal for many sites to support backwards compatibility. Instead, stuff breaks. This is why people are so hesitant to move to php5, perl6 etc. spamassassin should not follow these examples.
So why wait until now, long after 3.0 is set in stone, to complain about this? The whole point of a major version change is to allow breaking compatibility. (The time spent supporting legacy stuff is time lost for creating new features.) You know because of that number change that things are going to break, so you start doing your homework early, before you're backed into fixing your own stuff to comply.
At this point the horse is out of the barn, so the admins who weren't paying attention are naturally going to have to play catch-up. It's important to inform your PHB's that tracking the development of the products you support is a big part of your job.
Mind you, I'm not arguing against the specific feature. I'm just saying that if a feature is important to you, don't assume that it's important to anyone else, or that someone else is watching your back for you.
