I wrote a proposal for AP extension which may unlock direct support for lightning payments in Fediverse: https://codeberg.org/fediverse/fep/src/branch/main/feps/fep-0ea0.md. It is not designed specifically for LN, but for all types of payment methods. The only requirement is that payment target must be encoded as URI.
Do you know if it is possible to represent split information with URI?
I'm going to support this extension in my software, maybe other developers will also implement it, eventually.