Thanks! I skimmed the papers, some comments below.
The 1st paper you gave has a nice explanation of the original method by Gugger, I find it easier to read. @tl121 check out section 3 (“BTC to XMR atomic swaps”) in Hoenisch & Pino (2021) “Atomic swaps between Bitcoin and Monero.”
It highlights the problem of fees on BTC and how Bob could be exposed to a draining attack because he has to go first. IMO it’s less of a problem on BCH since our fees are significantly lower (also helped by the contracts being smaller). The above paper proposes an alternative where Alice goes first by funding XMR output, but it depends on having adaptor signatures on both chains (as opposed to just on BCH/BTC in the original protocol), which is pending more research.
The 2nd paper needs capability to pre-sign XMR, which is not supported at the moment.
The 3rd paper relies on some generic crypto magic which goes over my head but it seems to be universally applicable and the transactions will look like ordinary P2PKH, so it is an improvement over HTLCs since it preserves privacy and transactions would be smaller, and also allows cyclic swaps: a multi-party chain of atomic swaps, such that either the whole chain goes through, or nothing does.
The 4th paper uses one-way payment channels to implement an interactive cross-chain swap. Parties simply update the channels in ping-pong fashion: transfer the currencies in small increments to each other until the swap is complete. This sounds promising, as we can have efficient such channels on BCH!