This is something I did look into for long time, we use the "solder down" spacers in some stuff, and press-fit could also be an option, but
There are some constraints why I pretty much excluded those:
1) press fit really requires the PCB to be perfect for the press fit and should it "fall out" once the PCB is damaged and can not be used any more
2) both full SMD and hole-and SMD solderable spacers - the look NICE but if you compare the PCB area they need it is almost the same for M2 solder down thing as M3 would require
from seveal vendors 0D is 6.2 for M2, M2,5 and M3 !!!!
only würth has this
land pattern 5.3 mm copper
those things are actually cool, I did rule them out as of "space" constraints..
if we add support for "solderable SMD spacer" - ok for 5.3mm footprint there is needed to change:
1) module PCB size about 1mm larger
2) move mounting holes and connectors about 0.5mm
adding 1 mm would not change module spacing, and the modules would still fit into inside FMC card (there was a bout 3mm space left..)
so the only drawback is that "useable free PCB space" between the connector on the same layer as the connectors will be maybe 0.5mm to 1mm smaller, the max PCB area for single large component (on the other side) would not decrease.
in ANY case the "soldered" spaced can only be on the BASE board, this must be forced that way.