Here's some immediate positive feedback.
I'm liking the automatic pick-up of syntax definitions in my ST installation already. Will surely motivate me to finally polish and publish a couple syntaxes I developed mostly for myself in the past few months.
I also think that the integration of the Command Palette with input handlers works quite well and is very transparent to the user.
I don't have the time right now to test this out more extensively, but I'll report back with issues when I find them. For now, I created a repository on the SublimeTextIssues Github org, so we can track requests and bugs more easily. You probably know the deal.