How about Trempler you facilitate?
idea #1
You come up with a fun DM/SP/SC/etc theme idea, and den write up a list of jobs we can choose from to complete the map? Make the job list first-come, first-serve, and participants can also pick a second job once they've finished the first one.
idea #2
Map-from-base is always a fun option, and makes it easier for us lazies join up.
yes you have to make the basemap
idea #3
75 brushes compo--based on the 30 brushes official TWHL competition. You have 75 brushes to build a functioning DM or SP map.