LUD18 doesn't seem to be quite as widely adopted from a wallet perspective1. It shouldn't be too hard to implement from a receiver side, but if not many wallets support sending it, it's probably lower on the priority list to support, if I had to guess.

Footnotes

Be the example... don't wait for other to be for you. Few implemented because they do not know the power of it.
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Good point, re-reading the spec I see some of the potential usefulness of it aside from associated arbitrary identity data on the invoice. Good looking out, Darth!