Hmm, wouldn't that bog down the code? I would say that supporting more than one language should only be done if it can be without compromising program size or speed. I imagine that the plugin engine will be one of the things that will take most time starting up each time you open EE. Still, I do indeed see your point. Well, I only have opinions here so anyone having actual know-how, would you please tell me if I'm right or not?
Actually not; Xchat has plugin interfaces for C (meaning, loadable plugins), perl and python, and they are all working as charm. Same for GIMP, which has C, python and scheme. There isn't any direct speed performance hit, and if the main engine is thought as "scriptable", that is, if it thought to feed output to a generic script engine and to receive inputs as generic incoming messages, plugin languages becomes more or less a matter of tastes. With C being a bit less portable (i.e if you write a C plugin you have to recompile it on all your supported platforms and add the compiled versions to the shipments).
About power vs. simplicity, once a language breaks the break even point (that is, is able to build a compiler for itself) there is no language "more powerful" than others. It becomes just a matter of user-friendly-ness in programming constructs on one side, and on application friendly-ness on how easy is to interface the application with the language. HERE you may have significant performance boosts, and even significant usability boosts. In example, if the virtual machine setup requires to reload the script from disk (either in compiled form or in source) and to setup the runtime environment at each run, or if you don't have callback hooks from the application to the scripts (i.e., you can only monolithically run a script), you can't possibly think about a "line plugin", that calls a script on each line, or on each modify. I am not sure about Ruby, but about Python, last time I checked, scripts may be fed in i.e. from memory strings, but execution had to be monolithic.
Btw, I delayed a test integration to provide self-installing packages of Falcon on all the supported platforms, so people in EE can just dl and install the dev falcon package for windows, linux or mac.