A compromise base solution for AoS and WHFB. I am learning Blender and trying to solve the round vs square bases issue. The system will, in its firsts iteration, have round disks with a connecting square peg sloting into either 20x20mm square or 25 mm round bases. Currently all even square bases should be available with all the round bases they convert too.
The inserts are avilable either as "perfect fit" or a 0.1mm smaller so you don't have to file anything off.
The.stl files may have scaling issues due to Blender(or my inexperience in it).
There are slots for magnetizing with 5x1 mm disk magnets, for the smaller models it may be appropriate to use 5 mm washers of magnetic metal in the bases.
This is still not done: things are missing and things may be wrong.