That bit of text was misleading, the plugins that would be closed source are not the ones that would result immediately from this project, but instead domain specific plugins that wouldn't have broad appeal. All the language plugins will be open.
I would gladly throw $50 to you if you released this under a MIT (or similar) license. Even if I never switch from vim, I feel my $50 would be well-spent bringing a (hopefully) awesome free IDE into the world.
If this isn't actually free software but only open source, I still might purchase a license for myself, but I think it's fair that this is mentioned upfront.