What coins will be compatible with MNX when atomic swap arrives?
I guess that it will be only bitcoin and in the best case scenario ethereum

As far as I know for atomic swap transaction to occur both blochchains must share the same cryptographic hash functions. Bitcoin is SHA-256 but Minex is modified Equihash(Blake2x) (PS. I could be wrong here. Feel free to correct.)
Equihash is only used for calculating block solutions. Transaction verification with its merkleroots are identical to bitcoin.