Sony games aren't heavy on mp much less gaas so their online may not benefit from bc.
And I have no problem accepting there is a good chance of BC or the goodwill they could get or even how much easier than ps3 bc it would be. But giving it as certain based on nothing is silly.
We have had Sony heads saying how BC was overtalked and underused as a reason they didn't put it on PS4 nor would add later. We had PS3 dropping BC without much issue.
Sony certainly could make PS5 BC capable and locking it with some service of PS+ or offering to easy port/crossgen to devs so they can either have cross sales as we had at the begining of this gen and even keeping username/save so people could migrate.
There is several options they could take that would benefit their partners more than just put free BC and no double dips.
Sony wasn't the only making remaster/remakes (and they selling a lot), they had a good bunch of 3rd parties doing the same.
Remakes and remasters are very different things.
Its why you see remakes of games from the PS2/PS1 era but instead remasters of games from the PS3. It will make zer financial sense makin remasters or remakes of PS4 games the PS5 and selling them. Especially when their direct rival is offering the same service free.
Sony downplayed BC this gen like any good PR team would d because they just couldnt get the PS4 to run PS3 games. That is not gin to be the case going from PS4 to PS5. As they are both X86 platforms.
Native BC is pretty much a given based on that alone and based on the fact that its something MS will obviously d and sony simply cannot be selling something their rival offers for free. This doesn't stop devs from still supporting their PS4 games. And there are ways to do that. A dev can offer a 4k upgrade DLC and sell that for $10 for people that already have the game and want that while also main a greatest hits version of the game with the DLC built in and sell that full game at a reduced price for those wanting to get it for the first time.
Get this though...... sony isnt in a bubble. There is MS. And we know they will do native BC.
This has nothing to do with remakes. Those will still come and they are nothing compared to remasters. And then there is precedent..... the PS4 is the only playstation console to be released without any BC support whatsoever. So if anything' there is more historical backing for native BC than not.