We know that Sony are working on allowing the cloud streaming of select owned games, this was already revealed in a blog post not too long ago. It shouldn't be much longer until we learn just how widespread this initiative is and how many owned titles will be streamtable via the cloud.
As for the ability to stream PS5 games to a PS4 or PC, we have no reason to believe that'll be limited upon the full rollout. It's restricted to PS5 for the beta, that's all we know.
We have different perspectives on their motivations. At least we won't have to wait much longer to learn more about their next steps in cloud gaming.
I just disagree that we have no reason to believe in my perspective.
Sony has made it abundantly clear that they do not want to disrupt the retail/digital sales market in place of subscriptions.
They have had great offerings in the sub space, but are staunchly against 1st party games coming quickly to these services. They want game sales 1st, sub sales second. They do not want to develop users who are dependent on their game sub catalog (like Microsoft has.)
Yes I'm aware Sony have already announced plans to offer purchases via cloud, which is at the core of my point, the lack of ability to buy games and stream is the holdup for device expansion.
In a world where all games can be played via cloud if you purchased them (and you also pay a sub fee to access,) Sony has way less reason to worry about "not selling someone a device."
But even then.. Sony ALWAYS wants to sell you Sony branded devices. That's not a strategy Sony is likely to want to give up any time soon. They want you to buy Playstation branded this, Playstation branded that, etc. One way to guarantee that is to... well MAKE you buy those devices to use their games/services. (oh and they want those products using Sony developed media formats, they are the kings of that)
I could see a multi-phase approach that will take years to get there:
1) Streaming remains only on PS4/PS5/PC (and possibly yanking PS4 support for PSNow at some point as they did w/ PS3.)
2) Sony gets a few partners involved with the "play your bought games via Cloud" initiative.
3) Sony them magically releases PS5 game streaming for the Portal but not PS4. They will use the "DualSense is key!" excuse for that, as they have for doing things like not letting you use DS4 on PS5 for PS5 games even though every game works fine with it. Why? Because they want to sell you Portals lol
4) Next generation Sony negotiates into their contract that all PS6 developers games will show up on PSNow if the user has purchased access. Sony is the one company that can probably get everyone onboard, at little to no costs to themselves, but doing it in the middle of a generation is a lot trickier.
5) Suddenly Sony stops caring as much what device you play on, now they have apps everywhere.
I still kinda doubt 5 though lol.
Sony has done well in the market by incentivizing new device sales, not embracing the "hey you don't need a device" mentality MS pretends to have.