Long-term incentive compatibility requires
that there be some fee pressure, and that blocks be relatively
consistently full or very nearly full.
I think it's way too early to even consider a future era when the
fiat value of the block reward is no longer the biggest-by-far
mining incentive.
Creating fee pressure means driving some people to choose something
else, not bitcoin. "Too many people using bitcoin" is nowhere on the
list of problems today. It's reckless to tinker with adoption in
hopes of spurring innovation on speculation, while a "can kick" is
available.
Adoption is currently at miniscule, test-flight, relatively
insignificant levels when compared to global commerce. As Gavin
discussed in the article, under "Block size and miner fees… again,"
the best way to maximize miner incentives is to focus on doing
things that are likely to increase adoption, which, in our
fiat-dominated world, lead to a justifiably increased exchange rate.
Any innovation attractive enough to relieve the block size pressure
will do so just as well without artificial stimulus.