So my question is: which blocksize related hardfork proposal has most support from core developers?
Also, I would like to remind that some of miners who are currently blocking segwit, explicitly stated, that they won't run segwit without blocksize increase.
They're mainly saying that as a way of exploiting the Core team for being stubborn. They explicitly state that they won't run SegWit without a blocksize increase because they never expect Core to actually cave in and do a hard fork so they can get away with taking a moral high ground.
Obviously no blocksize related hardfork proposal has support from Core devs, otherwise they wouldn't have written SegWit, they'd have written a blocksize related hardfork proposal.