This app was mentioned in 10 comments, with an average of 2.20 upvotes
Empire Deck Builder https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire
Also consider a GBA emulator, where age of empires and age of mythology are done as turn-based 4x instead or RTs
Something somewhat similar has been done before: https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire&hl=en
The game is still pretty simple however, and is a bit unpolished technically then probably abandoned. There is no victory condition either, just an eventual defeat and a point score.
Do you have an Android device? I recommend EMPIRE, it's a lovely mix of 4X elements and deck building card games in a fantasy setting. Games are fairly quick. https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire&hl=en_GB
I like the idea of it. 7DRL can generate some pretty amazing games, Hoplite being a great example. The trick with it is distilling game mechanics into crunchy bite sized bits. The problem with a 4X games is that they tend to have a lot of interlocking mechanics, which is hard to develop and balance. But it is entirely possible to whittle it down to 2-3 clever mechanics and pull it off. With respect to /u/pingpongpan concern about AI, I'd definitely have to say that it might be easier as a multiplayer or more of a PvE experience instead of a PvAI. There are some examples of these types of games, but they're hard to find:
10 minute space strategy condenses the experience down to the basics
Star Chamber abstracts a lot of the 4X experience into a deck builder, but still retains the flavour.
The tragically blandly named EMPIRE reduces the mechanics down even more, and adds deck building mechanics (of the Dominion variety, not MTG like Star Chamber).
I'd be very interesting with what people come up with.
Yes Concrete Jungle is on mobile. I believe you are talking about https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire
I've been meaning to check it out.
God damnit. I really have to stop hoping it becomes easy to find...
https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire&hl=en
Empire: Deck Building Strategy Game
https://play.google.com/store/apps/details?id=com.crazymonkeystudios.empire
It's been a while since I played it, but yes, 4x deckbuilder.