Thanks for the reply !
“It would be possible to switch to static lighting for overflow lights but I don’t think it would be very useful. One of the defining properties of Stationary lights is that you can change their brightness and color at runtime”
This is not needed for static archviz. I just need soft shadows that are baked but a light that still triggers the sss. I wouldnt mind having a special advanced flag for that, so basically normally, it switches to dynamic, BUT when you activate that special archviz box, it bakes shadows while having the direct light component still dynamic.
“Note that right now, you can make them switch to fully lightmapped yourself by changing the overflow lights to Static.”
But then its like using static lights right from the beginning and I wont have a reaction on the sss material 
Sorry, I know this seems to be a super special weirdo case 
But I could imagine that it would indeed be very beneficial for archviz, since reality doesnt care about stationary light overlap 