Will they try and tie Planescape into that? Seems with the discussion on alignment and shift from races to ancestries, that this makes Planescape even harder to redo. But Spelljammer straight forward.
TL
R changes to focus on alignment won't make Planescape a difficult setting to redo.
I don't think any of the changes to alignment, whether it be the one about alignment being strictly a Role-Playing Guideline, or separating alignment from PC races automatically excludes Planescape. Alignments were quite tied to Immortal/Alignment-Paragon creatures like Fiends and Celestials, which were never PC races in the standard Planescape material. I definitely got the impression that the new outlook on alignment doesn't apply to those creatures. And even with those races there were the rare fallen celestial and risen fiend.
It may have had various 2e'isms (Level Limits! THAC0! Racial Class Restrictions!) about certainly PC races like Githzerai (CN) and Githyanki (LE, and in a product outside the core setting boxed set), both those were outright ignored in most cases, even though their entries allowed for some flexibility beyond the given alignment. Tiefling which Planescape first introduced, were never tied to an evil alignment, they might have had the Not-LG restriction in one of their writeups, but it might have been just some excuse to exclude them from being Paladins in the 2e rules (unlike many 2e races they could be almost every class in 2e). Tieflings might canonically be the first PC race that had NPCs of non-binary genders, as far back as the 90s. Bariuar had some pronounced gender differences between male (horn attacks) and female (skill and save bonuses), as Goat-Centaurs they're sort of the third wheel race of the setting and ret-conning Bariaur to all have the same abilities regardless of gender won't kill Planescape as a setting.
Alignments were quite strongly tied to factions, but factions were tied to philosophies like Solipsism, Theism, Objectivism, Nihilism, Authoritarianism, Anarchism, Fatalism and so on. One certainly could map certain alignments to some philosophies, as some factions are alignment restricted and others were permissive to all alignments.
As a setting Planescape leaned heavily towards Roleplaying instead of mechanics, despite the main designer having worked on a system like Rolemaster. When it got rules-heavy it was a lot of RAW things like "doing this thing in that plane": your +2 sword from the prime material plane is non-magical on the outer planes, because it lost one + from the astral, and another plus crossing into the outer planes or the Dimension Door spell doesn't work period in Sigil because that spell crosses into the Ethereal Plane and Sigil is cutoff from the Ethereal Plane, and other convoluted rules. I'm definitely of the opinion that you could and should throw out all of those rules, and Planescape would still be Planescape without them.