Well, putting the entire blender inside a web browser is an easy task. The challenge arises when you have to deal with security.
As .blend files allow Python Scripting these scripts must run inside a sandbox so the plugin can be guaranteed to be safe. Among other things, a sandbox prohibits the built in script to read the hard drive which in turn prohibits the script to include external scripts.
You take that out and you have a major security breach that is so easily exploited I don’t think anyone should risk.
Asking the user if he wants to view the file contents so the sandbox is disabled for some files isn’t that good either. Someone could easily upload an exploit to a well known model database site and… well… disaster!
BUT, an embed plugin that allows you to change the file stored into a web server could be fantastic! But IMHO that shouldn’t be Blender’s goal! Maybe a Mozilla plugin… but not the main package - and doing so, once you got a working web plugin and a working constructor interface is quite straightforward.
And there is also another problem: each browser window is another browser instance, and right now my only firefox window is using more than 50mb… and I just spanned a blender session… it uses only 11mb…
Of course when you actually get something in your blender workspace the space it uses get bigger (I don’t know how much bigger though). But I don’t think the amount of memory required to say “hello” to blender to be increased by a factor of 5 is something users will like.
BTW: I’m writing a new web plugin for blender for gecko compatible browsers (ie, any mozilla and webkit based browser, including apple’s safari). It should be in alpha stage soon (I can’t tell you how soon yet).