So, one very large transaction with numerous sigops leads to the quadratic growth. Hmm, so blindly increasing the block size is asking for trouble. How many of these troublesome transactions are launched against us recently? Or is it an unexploited vulnerability?
Perhaps we could increase the block size *and* constrain sigops/transaction until we get SegWit out the door?
Well the problem is only minor at a 1 MB block size limit. Segwit should scale it down and make it linear. It should be released in April (from the initial estimates), so I don't see how you plan to deploy the block size limit and a sigops limitation in <2 months.
but the block would get orphaned?
No, why would they?