But define mainstream. I thought 'masses would use bitcoin without knowing it'
Whether or not they realize they are using the bitcoin blockchain will not matter as much as if the blockchain will be able to scale to handle the transaction load and be able to pay for security in the future. If everything is handles off the chain because of Bitcoin is still in its training wheels than we have defeated one of the main benefits of bitcoin altogether.
Small blocks propagate faster, so there is less chance of orphaning them.
This will incentivize miners to have fast and reliable uplinks and thus in turn benefit propagation. Some miners will have to make calculated decisions to either accept the smaller blocks with less tx fee reward and less likely to orphan vs other miners which accept the larger blocks to cash in on the larger reward. A Half filled 20MB block could get an extra ~1600 usd fiat reward which is starting to provide decent change to fund future network security ontop of the block reward.