That's my question too. Already in December 2017 there was this article from coinomi on Medium:

https://medium.com/@coinomi/coinomi-announces-support-for-bitcoin-atom-bca-bf666e1d5e7f

When trying to add this coin (yes, with newest version of Android wallet v1.8.0) I couldn't find it on the list. Also on coinomis website https://coinomi.com/ there are many coins, but Bitcoin Atom is missing.

Strange.