I too had been contemplating updating the CodeMirror submodule name and its side-effects. Merging the changes.
Have raised an issue to track the action items mentioned in the description post this merge.

We could have delayed this merge till the next release and give a heads-up in this release about the impending change; This could be a breaking change with some extensions. Also the three issues mentioned by marcel had to be verified before this change was merged.
I think we should revert this change for this release to allow extension devs enough time to verify their extensions or alternatively check the impact of this change before merge.
Created a revert just in case we decide to revert this for the release.
@prafulVaishnav @nethip

There's one extension that uses CodeMirror2 for literal access: Brackets-Themes by @MiguelCastillo - all the others only use brackets.getModule.

Knowing this, I think we don't need to revert the changes. Miguel is probably pretty fast in updating his extension so it checks whether CodeMirror2 or CodeMirror should be used.

Point 2: We don't really need them (it's a "nice to have" and nothing else) as we can simply leave the requirejs rerouting in.

Point 3: That's just our infrastructure and it's very easy and non-breaking to do.

@marcelgerber Thanks for roping me in. I will change update as soon as this is merged in. :) Thanks for the heads up.

Thanks Marcel, i'll run a search for the usage of codeMirror2 on the source codes in the extension registry just in case and update. If the extension usage is proper, there would be nothing to worry about this going in the release 🐹

Alright, I just created a PR that's ready to be merged in when this is merged. MiguelCastillo/Brackets-Themes#115

@MiguelCastillo This PR is already merged, but it's not yet part of a Brackets Release.
One other thing you could possibly do is check whether CodeMirror2 still exists and use the appropiate directory based on the result. Just a suggestion, though.

@abose That's actually what I already did, but nothing to say against a second pair of eyes :)

@marcelgerber oh man, I must be going crazy. I could not find the merged comment! I see it now that I went through the thread in more details... I wondering why I couldn't see the merge button :)

@MiguelCastillo Notice though that your PR will only work in Brackets, so better set your package.json's minimum Brackets version to 1.4, too.

That's why I suggested conditionally detecting what path to use above: It will still work for both versions post- and pre-1.4.
In order to make that work, don't yet change the brackets.getModule paths - CodeMirror2 will still work fine for now.

@marcelgerber Thanks for fixing this. This was a very good observation.

And thanks to @MiguelCastillo and @abose for collaborating on making sure this won't effect the other modules.

Since these are all architectural changes I feel we should use our slack channel to bring these up so that everyone can put in their opinions before merging these kind of changes to master.

@marcel, I ran a search on the extension registry for CodeMirro2 and it seems that all of them except Miguel's extension is using Bracket.getModule("path?Codemirror2/file") format. So this change would be safe for this release as you said.
I will go ahead and delete the reverting PR.