Yeah, I did not get that either. I also do not understand why the GPLv3 would necessitate a contributor agreement, but MIT would not. I always thought those agreements were necessary so that one institution has copyright and can change the license without getting approval from every author. That applies to any free license, doesn't it? Anyway, I think they just wanted to change to MIT before new authors commit without an CA, after which they cannot change it so easily.
Were these concerns over Light Table for internal use by these companies? If so, then that sounds a lot like ignorant fear-mongering, either by counsel or execs playing armchair IP lawyer. I understand resolving the "sales objection"; it's just disappointing to see these licensing misconceptions persisting.
We were hearing concerns that the CA was worded in our favor and was one-way, in that people could contribute and we could take their work and commercialize it down the road without open sourcing it.
That makes sense, but then it begs the question of why Light Table was originally distributed under the GPL, i.e. since it's built from EPL'd software... and the GPL is incompatible with the EPL, as you say.
Does Light Table's new MIT license insulate developers from EPL-GPL compatibility concerns that might arise from the EPL'd pieces (Clojure/Script, et al.) used to build it?
A compiler or similar tool doesn't generally affect the license of its output (some of them explicitly disclaim that), just as a text editor doesn't affect the copyright of a novel written in it. The GPL is much more widely popular than the EPL, and now that it contains comparable patent language it is probably a better license to use (when the EPL was first written it was primarily to address patent issues that the GPLv2 didn't cover). I would hope that projects that are using the EPL would now migrate towards the GPL where possible - strong copyleft licenses are inherently impossible to combine, so it's best if the community can standardize on just one.
The MIT license is compatible with almost everything - it's really very minimal, comparable to a 2-clause BSD-style license. There is no problem combining MIT licensed components with EPL licensed components, or with GPLed components. (Of course there is still a problem if you want to combine with both at the same time)
A CA isn't really necessary for GPL code as such, but changing license without one is a massive pain, so you essentially commit to GPL and its restrictions forever if you don't have have one. This has caused problems for other projects (I think KDE is an example).
Obviously this also means we can't move from MIT now either, but it wouldn't really make sense to, since you can't practically add restrictions to already published code. (Strictly speaking I think you could still use LT under the GPL if you wanted).
The GPL makes a contributor agreement necessary if the original developer wants to distribute a version that does not comply with the GPL. With the MIT license, the original developer can distribute a proprietary version without a CA.
