I think that they are remaking the editor in order to set some things up for a better future for construct. People thinking that scirra is doing a complete remake without having any plans to take advantage of that are fooling themselves.
A complete redesign of the editor means removing some limitations that have been stopping them do some things.
It is not only to make it available on mac and linux.
I think Ashley mentioned something about opening up the editor more to add ons. I translate that to myself with addons being able to create new gui elements in the editor.
It would be particularily awesome if the author of Q3d for example gains the access to a level of the editor that allows him to add 3d scene editing for example.
@jayderyu That is an interesting observation. It would be quite awesome to see how it goes. I think that Superpowers (another html5 game engine) uses node.js for interface and it seems very powerful in more than one ways:
It allows them to make the engine collaborative ! That is quite useful on gamejam events! Too bad there is no visual programming like in construct yet