Maybe an indicator of the total estimated processing time for a block could be added in the block headers, and limiting the efffective processing time to this.
or advertising the number of sig op in the block more explicitly from start, and limiting the number of sigop processed to this,as mining nodes are already supposed to know this, if a way can be found not using too much extra bandwidth.
Maybe we could activate segwit, implement Schnorr sigs, stop worrying about O(n^2) attacks, and enjoy the other benefits like Lightning, tree multisignature, fungibility, etc.
/common sense
even activating segwit does not stop worrying about O(n^2) attacks!!
people wanting to cause O(n^2) attacks will still do O(n^2) attacks
wake up to reality.
O(n^2) attacks are only allievated by those using segwit keys.. the thing you need to understand is attackers wont use those keys even after activation. so the problem is not solved.
its like not wanting gun crimes. so you make a law that creates a new voluntary gun shop to open whichs sells plastic guns that fire paintballs.
hoping everyone will buy these guns.
the thing you need to understand is you have not closed the normal gun shops or put rules to force the normal gun shops to close. all segwit has done is effectively say the plastic paintball guns are x% cheaper to use..... thats it