5. Regarding Microsoft, I don't think anyone doubts that they'll be more profitable without a console, because after almost 20 years in the console business, subscription models are about the only thing they have to show for it. Regarding Sony, what leads them to doing what they are doing is Microsoft's direction. If Sony allowed Microsoft to establish themselves as the leader in subscription services, then Sony's profits would eventually begin to suffer. The major players' assumption that streaming and the like is the future may all be wrong, but nevertheless it's what they believe in and that's why they go where they are going.
I don't think it's about streaming subs. Streaming games is a gimmick. Wii's waggle controls were more responsive. It's about game rental subs. It's also Sony's natural progression from the failure of putting Steam on PS3 and releasing a mid-gen upgrade alongside VR. If PC gamers refuse to go to Sony then Sony will have to go to them. It helps make MS's home console look even more redundant in comparison to going with PC. PC will have PC exclusives and multiplats, MS exclusives and delayed Sony exclusives. XB only has MS exclusives.
Also, a mid-gen slim model would be more popular with console casuals than a mid-gen Pro model especially since they have nothing to fear from a rival mid-gen upgrade from MS.
PS4 release (day 1) = Box Office
Streaming PS4 (day 1) = CAM pirate copy
PS4 rental sub (~1 year later) = Netflix/Amazon exclusive to PS4
PC/PS5 remaster (~3 years later) = Bluray Special Edition DVD
PC/PS5 remaster rental (~3.5 years later) = Exclusive to Sonyflix or PS5+EA Access/UPlay on PC
EA, MS, and Ubisoft keep their console game rental sub separate to their PC sub. Sony doesn't have a PC storefront so letting Steam and Epic handle sales makes sense. Once sales slow down, Sony would be better off selling rental exclusivity to EA, Ubi or MS to add to their PC sub instead of starting their own store/service from scratch with only 1 exclusive.
Once Sony has enough games ported, they can start their own PC store and rental service and leverage their console install base to take on Steam, Epic, MS, Ubi, EA and likely Activision too by then. They'll also be able to match MS and have same day PC release if the subscription wars heat up.