I've been nurturing the idea for over a year and finally got a small push so we organised one meetup last week in Thoughtworks office (
https://www.meetup.com/software-design-berlin/events/297343473/). There were about 30 participants, which I think is the optimal amount. Also see pictures on the event detail page. My plan is to have a meetup every month, but let's see how things go.
If you are interested and live close, please join the group!
Robin