Why the fuck would they memory hole LMoP? That's 5e content from CURRENT YEAR theres no wrongthink in there
They didn't memoryhole it, like I said before it was rolled into the newer adventure book Phandelver and Below. Yeah, they replaced it in the Starter Set with a new adventure (presumably because they think people are too stupid to figure out why it's called Dungeons and Dragons if you aren't immediately doing something with dungeons and dragons in it), but it's still available for purchase and likely will be for the foreseeable future.
There are enough rule changes that it is not backward compatible. It's as much a new edition as 2e or 3.5 was. And as far as I know, they're not going to keep printing any of the 5e books.
They'll probably stop selling the original core rulebooks, but I don't see why they'd throw out all the other adventures and splatbooks they've released. There are rule changes, sure, but not to the extent that you can't run a pre-2024 adventure with new characters; you just have to be sure to pick one ruleset and stick with it when it comes to things like combat or handling DCs. It's backwards compatible, but not forwards compatible; you should be able to use your old characters in the new rules (potentially with some minor issues), but you can't use new characters with old rules.
Honestly though, if you're dead set on using the new rules, I don't see why you wouldn't just start fresh with a new character and save yourself the headache. But anyone who's attached to their character likely won't want to, which may make them reluctant to switch over and could torpedo their whole relaunch. I dunno, I guess we'll see how it pans out once it's in people's hands.
You know what, I havent really kept track. What are the major rule changes here?
RPGBOT has
a whole massive article detailing all the changes between original and 2024 rules. The biggest change is how characters are created, as well as a lot of class updates, but there are some changes to general play rules as well. It's way too much to go into, so I'd advise just taking a gander at whatever you're interested in.