I agree with BlueScope ... Instead of reinventing the wheel, it will be easier to just use the right tool for the job you want to get done.
It seems to me that an RPG that is not ridiculously complicated in stats or overburdened with hi-res graphics would be totally possible.
There are a lot of useful links in this Scirra forum topic about making & using tile-based maps in C2: http://www.scirra.com/forum/array-tile- ... 49692.html
Since your resources are not self-contained in an exe, but have to load in a browser, you have to be especially careful about how you use images.
However, when comparing C2 and RMXP, for instance, you would be able to pull off much more interesting physics dynamics with far less effort in C2, than you would have to exert into perfecting RGSS scripts in RM. So turn-based RPGs wouldn't be worth it to attempt, but more action-oriented ones, like Zelda, would be more up your alley.
One interesting thing is that some people are also using C2 for making Adventure (point & click) games.
So, say, if you wanted to make a game with a rich story, that uses interesting physics or dynamics for puzzles, you can potentially pull that off much more nicely in C2, than you would in RM*.
All in all, C2 is better suited towards action-oriented dynamics, so that's the engine you'd want to use for that.
If you wanted to make a typical tile-based & turn-based RPG with no focus on physics/action-oriented gameplay, you'd probably be better off with RM* or something similar.