The installation of Plus can't rely on some files be at the server. What would happen if the server goes down? And what if the user can't connect to the Internet when s/he want to install Plus?. The best is have all inside a single exe installation file, as it's now.
About the ability of select what feature to install, I don't agree with that. People will complain saying: "hey this doesn't work for me" just because they didn't installed that feature. Remember, people install thing too fast (next, next, agree, intall), without reading and they don't remember they didn't install that.
Also, if I'm not wrong, there will be a section at
msgplus.net where people would be able to download plugins.
About the scripting language. People would have to learn it, so why not learn VB (or VC)? VB is very easy and you have the
templates needed to compile the pluging. Including that feature into Plus would increase its size and using that you won't be able to do everythig you can do with "real" plugings. It would provide limited features. Also, someone made a pluging that offers a similar feature: It executes vbs files.
Search it. It should be somewhere.