What blocks me from digging into the source is mostly that even if there are separated components, I still need to understand all the aspects of Meteor. I can't just open the file and change it. Will it screw up the deploy system? Will all the data-binding continue to work as expected? Maybe yes, maybe no. Unless I totally understand the system, I can't really know.

You say "like using livedata (publish/subscribe) with Angular", but that's the problem I'm talking about. You need to tweak the system to make it work with Angular. But what about the hundreds of other smaller angular-like libraries? Or tomorrow's most popular one? I can't just <script src="it">, I'll need to create a meteor package and make sure it works good with all the rest of the system (Which unless I'm a Meteor expert, I have no way of knowing).

That could actually be a good blog article, "How to use MooTools, django template system and MySQL with Meteor". I.e. Going through what's needed to be tweaked to make it work. Compared to say, express, I could tell you use the mysql node library, normally include mootools in your html files and use mustache (Or whatever library already exist to mimic Django's libraries).