I think Sony will try and retain physical for a long as possible until the developers themselves deem it non-viable. It depends on the production costs and margins with wholesale retail in relation to the PS Store cut Sony take plus general demand. Not many retailers left on the high street now and those don't want to buy into dead stock.
To be honest, games are mostly so shit these days, there's not many worth getting a physical for anyway and even then, the disc is worthless by virtue of a game needing a mandatory update to execute. I think the PS3/360 was the last worthwhile generation for collectibles and with Microsoft trying to kill off physical for the past 9 years and Playstation only having a few tangible exclusives worth picking up physically, it's basically curtains.