Worth commenting that I'm not sure if Taproot threshold signatures will have a lower onchain footprint, like Taproot aggregate signatures do (I can't read the FROST paper, to be honest).

They do have a lower footprint. Frost signatures are the same size as musig2 signatures, which are themselves the same size as "regular" schnorr signatures. That is, they are all 64 bytes.

One of the difficulties with using frost is that it doesn't support "bringing your own key." If 3 people want to generate a 2 of 3 "frost multisig" together, they cannot each independently generate a keypair and then "combine" their pubkeys together. They have to come together to generate a keypair together in a kind of "key generation ceremony." The ceremony involves doing some math that allows every keyholder to ensure everyone followed the protocol properly so that they all know for sure they'll be able to sign later.

Not only is frost not standardized yet, there is also not yet any standardized way to do the key generation ceremony. And if companies like Unchained and Hodlhodl want to support this new form of multisig, some of them will probably have to change how they do business. Any of them that ask their users to provide 2 keys and let the company provide the third can't really do that anymore. They'll have to participate in a key generation ceremony that involves interacting with both users to generate a key and do the aforementioned math to ensure it's safe.

It's all quite involved and I don't expect much fruit to come out of it anytime soon. "Regular" multisig works well so I don't see much motivation to code up the fancier version that taproot enabled. Consequently the number of people working on it is small, and progress is slow.