This seems like a potentially much larger topic than the "little things" of #49298 so I've made a separate issue for it.
I have a trie data structure that works over net.IP with lots of bit twiddling. It works well, but of course I want to switch it over to netip.Addr, and benefit from performance there. However, there currently is no way of getting at its internal uint128 guts, or doing any arithmetic therein.
Seems like this would be a nice thing to add. I don't have a concrete proposal for how to do this yet (so this isn't a "proposal: " issue), but I thought I should still start the discussion.
API wise, I was hoping some of those uint128 accessors could somehow get exposed, so I could index bits and and, or, and xor limbs together without having to drop down to bytes or roll it all myself. But I could also understand if that's not desirable in general to do.