All approaches are equally viable and have pros and cons. I use both MILS (on both 36 x 36 and 48 x 48 baseplates) and non-MILS constructions. The differences seem to focus on making collaborative displays seem more cohesive and professional looking.
Yet there are too many differences in building style, individual part inventory and building sizes that we produce to impose any overall display standard, except where we intend a large, semi-permanent display.
With the differences, pros and cons in mind, MILS should only be a standard in this one case, and even then, because of the part intensive nature of MILS as the very foundation of these collaborative displays, it’s very much a LUGBRICK issue in my mind unless collaborators build their own.