I can 't imagine Sony and MS making that big of a mistake to ignore B/C for this generation. While I understand the PS3 may not make it, PS1/2/4 should all absolutely be there.

X86 architecture doesn't guarantee BC, it's not that simple.

Nobody realy cares for BC, its a nice topic of discussion on forums but it makes almost no actual difference on sales or on a console popularity. Average consumer doesn´t even know BC is a thing if the guy on the store doesn´t tell them. 

But as Sony CEO said in the past, BC is often demanded, but rarely ever actually used apparently. Which means that while there's no technical reason why there's no BC, it has no guarantee to be included into the PS5. For MS, it wouldn't make sense to leave it out, but for SONY, it's the other way around. 

I don't see why they'd forgo making this gen not B/C during next gen. It's been made possible this gen with MS to a large degree, so I can easily see both parties making it very possible next gen with current gen titles. What remains to be seen, is if they will not only make all current gen titles B/C for next gen, but also allow for many more options, like settings for visuals and even more performance options, like the few we've seen this gen already with current gen titles.

Many forget wiiu had full BC as well. Basically if it’s hardware based you don’t need to ask permission but if it’s emulation you must. And PS5 and nextbox will probably be BC becuase the architecture is much more pc like and less custom

I hope they find a way next gen to get 100% BC because they are some games xb360 games that I want to play on xb1 that at the moment I cant play such as import tunner. I dont think that game will ever be BC.

But it does:

It’s no suprise Call of Duty be among the U.S. top 10 best-selling titles of the month. The annual military shooter franchise is among the top-selling games of every year. But it is strange to see one of its older installments hit the charts. According to The NPD Group, 2009’s Call of Duty: Modern Warfare 2 was the No. 8 best-selling game in the U.S. in August.

So, uh, why? Well, the Xbox 360 version of Modern Warfare 2 became backward compatible with the Xbox One on August 28. This drove sales of the shooter to an insane degree. In July, Modern Warfare 2 was only the No. 321 best-selling game. This growth shows that many people just want a way to play older games that doesn’t involve keeping an obsolete console around. And this doesn’t just apply to the old games they have laying around. They’re willing to go out and buy them (or stay in, if they’re using the newfangled internet contraption to make digital purchases).

- "Can MS & Sony just simply make next gen fully BC? "

simply, yes because the architecture of the hardware will be the same

It isn't as important as exclusives and new game lineup, but it's absolutely an important feature. Sales numbers for newly B/C'd games shows that. I understand why PS3 BC isn't possible on PS4 natively, but there's no reason why PS4 shouldn't be B/C on PS5.