Expand access so everyone can play, always.
Two strangers meet while hiking. As they wait for their dinner to cook one offers a game of cards. They play, bond, and depart the next day.
Smart phone games can rarely offer the same spontaneity. To share a game both players have to have it installed. Even though access to Internet is common, it is not everywhere.
Low income gamers and children buy budget tablets which don't have a cell radio. Others may buy a mobile phone but still don't get the data plan because the yearly cost is too high.
Cell phone services for many providers often end at national boundaries. Travelers can either pay extra fees, or only use wifi. If a gamer is relying on WIFI, their connection at the hostile is iffy. The routers are often overloaded, or don't reach past the common area.
Many cell phones also do not allow users to expand their storage. This leaves people budgeting what they install heavily. They might not want to clog up their storage with social games just in case they run into someone who wants to play.
There has never been an excuse not to provide this feature. Android and desktop platforms both allow side loading of software. HTML5 has also come a long way. With the Google Web Toolkit we have fewer and fewer reasons not to make thin clients for our multiplayer games.
Void Control is a game being developed by Curious Origins, however the framework it will be built on, which will allow this
Internet-free spontaneity, is possibly more important.