I am also very interested in the topic and eager to get informations about actual "real" tests that are going on. According to
this Spanish article there were tests with Bitcoin, Zcash, Litecoin, Decred, ARK and Vertcoin, some weeks ago.
The traditional atomic swap model supposes one multisig transaction per chain. That obviously isn't enough for high frequency trading but would enable the typical use case of a trader that wants to "ride" bullish and bearish cycles of distinct coins. For higher frequencies, one could use LN, or maybe even a specialized pegged sidechain in the future (RSK?). For LN, however, I think it would be used mainly for small exchanges of less than 50-100 USD because of the slightly increased risk.
By the way: There is a
atomic swap system that works for two years now used only by two small altcoins but supposedly could be adapted to
Bitcoin-based coins. I have recently downloaded both blockchains to test it soon, if I am successful I'll report results here.
For XCATs you'll need to run a full node for each cryptocurrency you are trading, e.g. you'll need to run both Zcash and Bitcoin core if you want to exchange those two cryptocurrencies. You'll also need to run some middleware that connects everything, see
https://github.com/zcash-hackworks/zbxcatThanks for pointing me to that software, will try to test it. A question arises: Would it be possible to use SPV wallets like Electrum for atomic swaps? If yes, then the storage problem would be solved ... Another idea for mass adoption could be if "hybrid semi-centralized" wallets like blockchain.info included an atomic swap feature, as they could manage "chain handling" for end users.
Merchants that want to accept multiple cryptocurrencies and convert them into Bitcoin for e.g. paying taxes in Bitcoin will probably have fairly significant disk storage requirements.
If SPV wallets are not possible, Bitcoin 0.11+ style pruning could be the solution for that - a merchant then could easily accept up to about 100 currencies with ~1GB storage use for every chain.