I read Ejecta doesn't support patterns yet, which is a blocker (Tiled Background won't work without it). It also doesn't support C2's memory management for large projects. However if it supported WebGL it'd use a different renderer anyway which supports both.
If it already supports AJAX and Game Center, and it gets a working WebGL, then it's a pretty interesting option. TBH I'm getting a little frustrated by slow progress from appMobi and Ludei on all three of those, so adding optional support for Ejecta would be nice.
It looks like it also has WebStorage and decent Audio support, but it's still missing something that could be used to make letterbox mode, it strangely seems to be missing the deviceorientation event, and it looks like it ought to have support for suspend and resume events which it doesn't say it does.
Still, potentially promising...