Addons: parameters and return values

I think it would make add ons much more useful if you could pass parameters to them through the RunAddon command.

It would also be useful to be able to get a return value from the add on (ie the result of a calculation) that could be used in the rest of the workflow.

In addition to that, can you let me know what methods are exposed to addons so I know, for example, how to call a specific action/step or workflow from a c# addon?

Thanks in advance