I think of creating new accordion plugin (I know there is one) but I want to know if anyone would be interested in such plugin. You can watch working example at:

http://www.ai360.pl/projects/airanimation/bh

click "start" at the bottom and then choose "Location" - accordion is on the right.

Accordion is built from xml data file: http://ai360.pl/projekty/airanimation/bh/accordion.xml so it could be created in easy and fast way with basic knowledge of xml. Accordion will have its own config section so every feature like width and height accordion, tabs, background color, icons etc. can be easily configured.

Is anyone interested? Does it make sense to start working on it?

Accordion is one of the way you can show stacked list of items. It should be helpful which IMHO means clear. I dont think 200 items on any list could be helpful - perhaps you will waste too much time to find item you are looking for. If you design any GUI controlls you have to make a decision what kind of controls you will use depending on space you have in your project. But for long lists with many items I can make scrollable pannels. (Personally I dont like it but if it is necessary...)

I also plan to make one-level accordion - I don't think accordion is a good menu for nested sets.