This gen is receiving a mid gen upgrade and the PS4 PRO is 100% backward compatible with the regular ps4. 

So let's say in 4 years they release the PS5. I expect the jump in power to be more then the jump we're about to get. But it's still a jump in a similar time frame.  

With the ps4 using mainstream pc parts and I presume (?) x86 architecture,  shouldn't it be easy to build so that every ps4 blu ray will play on it?  Or any psn download?  

Would all these games need to get re-licensed to be allowed legally on ps5? Or can Sony just make it backwards compatible and there's nothing third party's can do about it?  

I'm not claiming I know the ins and outs so if you do give me your thoughts.  Or if you have an opinion on the matter let me know! 

If it uses the X86 architecture, and this is like 99% sure, it should be backwards and forwards compatible, games should run better on the new hardware (or at least more stable and load faster) automatically because BC is not Emulated, like in many other cases in the past.

I don't think there's much of any doubt that the PS5 will be backwards compatible.

Actually, I wonder if it could be totally backwards compatible. Like, with every Playstation home console. It should be strong enough to just brute force the PS1-PS3. I don't know if they'd actually do it...but it would be great.

It should, the only things that probably will not work is games that get delisted.

I doubt theyll do it, since they sell those games on PSN, and the ps2 games in PSN are upscaled (better) versions, they just want to gain that money from the old gens, but you are right from PS5 and onwards, we won't have to deal with that again.

There is a chance tough one of the future consoles might not have an optical drive anymore, probly not the ps5 but its always been a sollid theory that whatever happens on PC will eventually happen on consoles and all-digital has been a reality on PC for some time.

But I think thats the only chance for incompatibility I can think of.

90% yes and they should ad 3,2 & 1

If they don't, they will get called out and exposed as complete liars since their excuse this generation was switching architecture. There is absolutely nothing preventing the PS5 from playing PS4 discs and everyone knows it so I expect that they'll have to allow it going forward.

I'd love it if they added BC and then gave players the option to upgrade for a small fee.

They sell San Andreas on the store for $14.99 in 1080p with trophy support, and if you have it on disc you can play the normal PS2 version. But for $5 you can upgrade to the digital version.

If it has the disc drive and the X86 architecture I wouldn't see why not, except for PS now perhaps.

I think the expectation is that both Playsaton 5 and Xbox Next will be 100% BC.