Some of those architectures really need to be allowed to die. VAX was discontinued in 2000 and was on life support since 1992 when it was superseded by the Alpha.
If it were free it wouldn't matter, but as you say its held up progress on architectures people actually use.
The way netbsd does GCC updates gives a really wide margin for figuring out compiler issues:
- Copy existing compiler into gcc.old
- Add new compiler as "gcc"
- Switch architectures one by one
If one architecture is left behind it's not a big pressing issue, you have until the next GCC update. They're done once 2-3 years hopefully so the GCC VAX issue taking 6 months to resolve wasn't close to being a problem.
As for removing architecture support, as long as it builds without extreme intervention, the non-VAX crowd is going to leave it alone. The VAX code is mostly separate in its own directory so doesn't get in the way.
The people who care about VAX within NetBSD are very knowledgeable and it would be a shame to alienate them without a good reason. They've contributed a lot of non-VAX stuff too.
If it were free it wouldn't matter, but as you say its held up progress on architectures people actually use.