Sales of ps4 hardware will drop fast, but with easier cross-gen development it can keep the ps4 alive much longer and keep selling games for a few more years. There is less incentive to drop the previous gen quickly this time.
80% of sales are standard ps4
20% of sales are ps4pro
8% are upgraders
So 12% of "new" gamers got a pro
The 8% are obviously buying a ps5, it indicates they have the disposable income to upgrade every 3-4 years.
The 12% new gamers who just got a pro is a wildcard. But it would contain a bunch of gamers who usually wait for mid-gen for a big library of games available (because no BC), and they might have decided to spend a little more for a Pro. There are also those who got into VR with the success of PSVR it's a no brainer to get a Pro. The rest can't be a big enough number to slow ps5 upgrade speed.
The 80% are following the normal course of generations, ignoring the mid-gen. I.e. Power was not worth spending more.
What should drive the transition is sony coming out with next-gen only exclusives with 90+ metacritic. But with full BC it's already in the bag with a big library for early adopters.
I used to think mid-gen would cause a problem with nextgen adoption, and I don't think so anymore. The BC will help them maintain their current userbase, and the exclusives will convince them to upgrade. The stronger cross-gen offering will keep the lower income gamers happy with the original ps4 until they are ready to upgrade. PSNow (either streaming or download) is increasing access to games for a lower price, again keeping them on the platform until they are ready to upgrade.