Steven Roose and ReardenCode have published a BIP for TXHASH. This proposal has been discussed since at least 2023 and was assigned a BIP number in 2024. It is now merged into the BIP repository.

Roose gives a nice explainer of TXHASH in this @btcpp video:

TXHASH is a kind of "templating":

the use of covenants to construct a series of either entirely or partially pre-specified transactions that is committed to in an output.

Similar constructions to this are currently possible by pre-signing the transactions. The drawback of this is that large signature and public keys have to be put onto the transactions and that the entire transaction has to be specified upfront. Proposals for better transaction templating constructions will mostly focus on being less costly and more flexible with regards to how complete the specification of the transactions has to be.

TXHASH is a soft fork proposal which, if implemented, could make it easier to run a lightning node or an Ark, and if combined with some other new op codes could make it easier to run statechains and vaults. Shinobi wrote about TXHASH last year, although I didn't find it terribly helpful.

A quick check of the Covenants Support Wiki shows us that people seem to generally be okay with TXHASH, even if they don't prefer it quite as much as something like OP_CAT: