What helped this generation is that current gen consoles didn't launch with backwards compatibility. We saw Last of Us Remastered, Gears of War Ultimate Edition, Uncharted collection and then Microsoft released BC on the Xbox console. So going forward, people are going to expect BC from Microsoft going forward and it's possible that Xbox One games might be available day one on the next gen Xbox console.
If Sony comes out and announce the PS5 and it doesn't have BC, I think they will be a big problem for them next generation if you were forced to buy the games over again. Not only that, people are going to want to play the PS4 AAA exclusives on the PS5 with a higher resolution and frame-rate.
I could be wrong, but I think it will be a back look for Sony.