I'm not sure, if I missed something, but why isn't block size limit defined dynamically based on previous usage (plus some safety margin)?
Is it impossible to implement a self-regulating block size limit mechanism similar to the way difficulty is adjusted, which allows the block size limit to be increased and decreased based on "demand"?
I'm not aware of more recent discussions but I found the first three pages of
this Feb 2013 thread good food for thought.
Decentralization should be preserved by all means possible, because it is the very core that ensures the safety and thereby the value of Bitcoin.
There's risk in everything and nothing is absolute. This attitude would yield the obvious answer: "Don't ever raise the block limit at all".