Not sure how many people would come to a freecad developer (?) conference and how large you want to scale it, but maybe it makes sense to use the leverage of a bigger conference and held a FC conference as a sub-track.
For example, here in Austria we have the Linux days and Linux weeks (https://www.linuxtage.at/ https://www.linuxwochen.at/wien/
) and there is now a python track in addition and we also had once a mini Debconf in Vienna, which was a nice little conference.
Therefore, it would probably be possible to have something like a FC conference at the Linuxwochen in Vienna.