Having taken a quick look at steem monsters, I wonder if that is just the start.
As you say gamers like 'rewards' & swap & sell them.
All steem needs is a hit game. But they are difficult to develop (game play) and take time to build a user base.
Perhaps it would be of benefit to steem to get developers to "port" games over.
We used to 'port' applications from dos to windows, and windows to Mac.
I'm sure there are technical difficulties, but maybe worth the time & effort
Imagine a hit game, with 100K or 1mm users hitting steem blockchain. wow
Time will tell