I've been playing agar.io for a while, then switched to chopcoin.io, and later switched to bubble.am. The last one is much faster, has more food, and has nothing
* to do with Bitcoin. Chopcoin is too quiet to be a good game, and that hasn't changed since it started.
Recently, I have discovered slither.io, and since then I haven't touched agar anymore. And that brings me to this quote:
Since agar and slither are both popular games, we can promote bitcoin on a vast scale if we have something similar to slither.
I don't think Chopcoin.io has contributed to promote Bitcoin at all. This is not a complaint about Chopcoin, I think it's played by (a few) people who like Bitcoin already. Not by "new" people who have Chopcoin as their first Bitcoin experience.
For the same reason I don't think a Bitcoin-slither will contribute anything to promote Bitcoin.
If the original agar.io or slither.io games would start supporting a Bitcoin-game, it's a different story. That would reach a large group of people who have never used Bitcoin before. On top of that, it would instantly have a game with a large population of users.
*bubble.am offers to exchange "points" you collect for Bitcoins, but they didn't pay out.