I've noticed this for a while, but in Monsters of the Multiverse, there is not a single monster that has the Magic Weapons feature. There is Orcus, who does have a +3 magic weapon, but otherwise, monsters that had the Magic Weapons feature in the past just deal some other type of damage now, often force. I will note that it is easier for players to get resistance to energy types (even force) than it is to get resistance to magic weapons (I think only a few class features will allow that).

Another place this is notable is in Van Richten's Guide to Ravenloft. When Curse of Strahd came out, it introduced wereravens to Fifth Edition. They functioned similar to other werebeasts, including the immunity to weapons that are neither silver nor magical. They got reprinted in Van Richten's Guide, with one change: now, they had no immunity whatsoever, but do have a regeneration which can only be suppressed by hitting them with a silver weapon specifically (magic will also shut this down). Wereravens will only die if they start their turn with 0 hp and fail to regenerate. I can only assume that One D&D will probably extend this change to the werebeasts in the Monster Manual. I should also add the Loup Garou from the same book also has that regeneration, with the added bonus that it can't be thwarted by getting hit by a spell.

Under the rules prior to those two books, once your martial character got ahold of a +1 weapon, they could reliably damage anything (which is good, casters are often seen as strong so limiting them with Legendary Resistance and insane saving throw bonuses encourages them to be more supportive), but when you consider that Xanathar's has uncommon magic weapons costing as low as 200 gp but an adamantine weapon costing 500 gp (when the former does everything the latter can and more), it does raise eyebrows from a design perspective.

Does anyone else have speculation or thoughts on changing what magic weapons do beyond adding a bonus to hit?

I expect a number of magic weapons will allow changing the damage type of your attack, that's what class features that made your weapons magical have been changed to in 1DD.

I rather like the potential variety of flavours that could give to magic weapons. Not just a bog standard +1 longsword, but a longsword of lightning (+1). 

For WH40k fans, wielding thunder hammers could be fun. 

Part of shifting from “counts as magic” to alternate damage types might be a soft nerf on the Rage feature so it’s less effective against high-end monsters. Plus it’s probably just a cleanup change as well, since I suspect a lot of people forgot the “counts as magic” clause when they were running the creatures.

I suspect items that grant resistance to force damage (brooch of shielding, items that come in a variety of resistance types) will see changes, since force damage seems to be their default for irresistible damage in 1DD.

Quote from Thucydides >>

Wereravens will only die if they start their turn with 0 hp and fail to regenerate. I can only assume that One D&D will probably extend this change to the werebeasts in the Monster Manual. I should also add the Loup Garou from the same book also has that regeneration, with the added bonus that it can't be thwarted by getting hit by a spell.

This is the same language they were using all along for troll regeneration:

Regeneration. The troll regains 10 hit points at the start of its turn. If the troll takes acid or fire damage, this trait doesn't function at the start of the troll's next turn. The troll dies only if it starts its turn with 0 hit points and doesn't regenerate.

Using regeneration in place of weapon immunity for werebeasts is probably a gameplay issue rather than a more general design issue -- it avoids the problem of having some PCs standing there being utterly useless while still making silver weapons important.