We apologize for the instability of composr.app and appreciate your patience. We are working on the statistics addon and trying to find an optimal way to store and render data. Unfortunately, we have yet to find a solution that can handle the traffic (and therefore, tens of millions of statistical records) of composr.app. We're working hard on one.
Ace and CodeMirror are the clear leaders in editors now.
http://ace.c9.io/
http://codemirror.net/
As Ace has massive backing behind it, and a long history that has clearly stabilised against an impressive and active Open Source project, this is what I think we should go with.
Finally, this one is implemented. It is on github in the feature__code_editing_update branch, which will be merged in for v11, which will be a relatively short development cycle. Thank you for the sponsorship Rishi, and sorry for the huge lead time. We're getting there though!
http://ace.c9.io/
http://codemirror.net/
As Ace has massive backing behind it, and a long history that has clearly stabilised against an impressive and active Open Source project, this is what I think we should go with.