Yes, they will need to be. ANY feat in any book right now is not compatible without an update or errata, for example. And that's from ONE playtest.
I beg to differ, but my reading is different. I read the options given at chargen with regards to feat as allowing "1st-level feats". Those are in my reading a subcategory of the overall "Feats" category, where you have "1st-level feats" "5th level feats" (to be published, or which may not exist if being "1st level" is just a designation used to identify feats that are selectable in the new chargen rules) "Feats where the requirement is to have STR 13" "Feats which requires you to be able to cast a 1st level spell"... A "1st level feat" is just a feat, who happens to match the quality of being "selectable at first level for rules that require a 1st level feat" which identify them as being selectable during chargen as the cuman bonus or with any of the new background. It doesn't make the other feat, that one might get from any other source, incompatible, just unwieldy.
Unwieldy, in that at the same table Bob could be using the original Lucky feat (3 points, giving "superadvantage") while Molly will have the compatible Lucky feat (PB points, retroactively grant advantage or disadvantage). I don't think it's incompatible as in "you can't play without houserules", it is unwiedly in that each and every character can have a slightly differing ability. Which, some would say, is great to make your char a special snowflake. It is also unwieldy in that both feats bear the same name (so groups will evolve name like vuman and the new Lucky feat will be called Cucky) and that we don't know (which isn't incompatible, just... unclear) if one can be both Lucky and Cucky at the same time. I don't see incompatibilities, it's just... cluncky as a hell. But it's still ONE edition, without incompatibilies so far.
Same, the "no critical from NPCs" isn't incompatible with adamantine armor. It just means that adamantine armor does absolutely nothing more than regular armor. Adamantine was just nerfed (and I except it either to disappear or we might see armies of enemies wearing adamantine since it's totally useless to loot it).
If you disagree, what feat level is Elven Accuracy for example? It's not a PHB feat so not currently slated for a playtest revamp.
It is outside of the "leveling" restriction that only appears with new backgrounds, like the number pi is outside of the "even" or "odd" designation. Sure, you can't take it with the new rules as we see them so far, because you an only take "a 1st level feat". But you can take it with each and every other possibilities to acquire feat you can come across, such as replacing an ASI. It's only when we get the playtest packet on the feats acqiusition that we may see incompatibilies. Which will have to reported as bugs in the playtest, since they break the initial promise of being "one edition".
I have low hope of them being able to achieve compatibility in the final product, but so far, I am not yet saying they failed. They just turned something simple to play into something that looks very unwieldy.
This is similar to the shift from 3e to 3.5e. They never did get back to giving out the errata or update on some of the books which came before 3.5e was released. They even at one point said by name some they planned to offer errata on, and never did. People joked when 4e came out "Well I guess we're never going to get that errata for book X."
They changed the edition number. You were either playing 3.0 or 3.5. You could try to mix and match, but you had to do it knowingly, with distinct numbers. Here this isn't an option, since it's all "D&D" from 2014 to 2024 and to the end of time. So basically they must maintain compatibility if only to avoid silly situations.