Thank you to everyone who responded to my poll. It looks like worldbuilding and language design have the same number of fans, and if all of you are involved, then a workshop would work quite well. Goodness knows I don't need to overwhelm myself with participants!
I'm going to begin the workshop in the beginning of December, date to be announced, to give the NaNoWriMo participants a chance to breathe a little (just a little!). My current idea is to run the worldbuilding workshop first, and then to do language design afterward: this seems a natural progression given the number of world factors that become relevant to issues of language design.
Anyway, I think I'll begin with an initial set of questions, so I'll be posting those first as December begins, and then picking up a little later once you've had a chance to formulate some answers.
As this is my first workshop, any suggestions are welcome! I'm looking forward to it.