I understood that it kills the devs and everyone using the tool, but why has it gained so much traction in such a short time despite Improbable being a relatively small company and why Epic is involved suddenly?
Epic is involved, at least in part, because Impropable Edmonton, now led by the former BioWare GM, works in Unreal 4 so they already have a pipeline for Unreal and Epic is supporting that, transitioning all other Impropable studios over to that same framework, at least that is what it looks like to me.
My overall impression is this though:
Open Source company TOS violations against Private Corporate company.
Which one am I gonna put more faith in? Yeah, Epic games, you should've read the tiny lines, get your people out but afaik the transparent company here is Unity, not you and this was self-afflicted due to lack of oversight by someone. I've heard the dispute over whether Unity changed their ToS last-minute to cause this conundrum, and while I haven't read it myself, I keep hearing accounts on it saying that what people refer to as "changes" was really clarifications, which is something Unity changed to their ToS
as Impropable started crossing their line and also that Unity had given them time to react to these violations, but Impropable kept ignoring their warnings until Unity pulled out.
This won't really change the fact that Unreal's toolkit has a way steeper learning curve. C++ sucks to develop in compared to C#. I would love if they allowed more languages.
Unreal 4's C++ support also sucks. If your code has faults in it, it's not just throwing errors or exceptions, the whole UE4 editor goes in lockdown. Besides that, documentation for Unreal is horrendous. Nobody, particularly not indies are going to use Unreal 4 without some face-to-face guide to make them understand how the engine works.