The problem lies on getting a 75% consensus from the miners
75% among just miners is way too low a threshold, you need strong economic support as well which is unlikely to happen at this point(SegWit is really the only proposal at this time with a decent level of support from the economy), and even then you probably want 90% or higher miner support in addition to a very long lead time(6-12 months) for any HF.
At least get your info correct.
The 75% he is referring to is if BIP100 was ALREADY activated.
The 75% is required, once BIP100 is activated, to adjust the block size up or down via coinbase voting, to be in the 1MB to 32MB range, with only a small adjustment each time.
Segwit has no such option, it's a "side effect" block size increase, if you use certain addresses.
So all SegWit does in reference to the block size, is give a new, non-adjustable, 'possible' larger block size.