We already have a plugin architecture; it's just compile-time not run-time. There are problems with run-time plugins (eg .so's) which hinder us from adding such support - mainly memory use due to symbol tables.
The reason why it hasn't appeared is due to a couple of factors:
1. We're not going to cripple the products by adding a plugin interface (ie, we won't add it if we can't find a way to do it without sacrificing the "normal user" experience - and that includes having to reduce caching space)
2. We're unlikely to do it without a "proper" way to manage plug-ins, eg emplode control. Without this, the number of plugin users would probably only be about 20 people and wouldn't justify the work involved.
Plugins are nice in winamp, etc, but they don't operate under the same restrictions as we do. If we can add them neatly & cleanly, we will do so. This is not saying that it'll never happen, but it takes programmer time, and there are much higher priority tasks to complete first.
Hugo