1) Develop Stencyl specific multiplayer functionality
Pro: No license fees to other companies, tailored for Stencyl strengths
Con: Unending development, poor functionality compared to commercial systems
2) Commercial Extensions
Pro: Robust multiplayer, shorter development time
Con: User fees (maybe Stencyl could negotiate a user discount?)
The best of both worlds would probably be to use a mature opensource multiplayer system like Red5. But Stencyl users would still need a host.
Maybe we should have a poll asking users who needs multiplayer, what features they need (ie number of total users, simultaneous connections) and how much they are willing to pay for it. Then Stencyl devs would have a better idea to pursue home grown vs. commercial extensions.
And again, great work! 
As I stated with previous post, I want to communicate with anything. Not just another flash game. So I want thing Stencyl agnostic, and also Flash agnostic. Lightweight and standard is the utmost concern to me. That's why XMLStream, AMF etc. are out of the way (it is not hard to write XMLStream analogy of the nginx+http_push_module, in node.js for example). My aim is to have flash client for ... virtually anything I want to.
With this solution, I can communicate with anything. I can even communicate with plain bash scripts. It is just the matter of a curl and some options.
So I would definitely vote for homegrown based on standardised communication paths (http(s)) (or existing one based on such paths, if it exists). But I fear the majority would rather adopt specialized solution.
And thanks.