EOSFinex is very interesting indeed, and when I thought about it I realized that Bitfinex is not just making EOSFinex and Ethfinex.. but probably going All-finex in the sense that they are likely to couple the two together. I mean, why would they keep EOSFinex seperate from Ethfinex, when both smart contracts platforms are perfectly capable of inter-exchanging. EOS and ETHfinex are likely stepping-stones to creating an all-in-one mega DEX.
Perhaps this is Bitfinex's strategy in dealing with DEXes. Since most are protocols, they are still dependent on parties to tie the whole bunch together in some way. That would make Bitfinex remain relevant in a DEX-future.
I guess they figure if you can't beat their (future) feature offering, better join em.