As suggested in some earlier posts, not a significant problem .. caveats
(a) seat certification needs to comply with the appropriate aircraft standard
(b) seat to pallet to floor load path has to comply with the appropriate aircraft standard
(c) stuff behind has to be restrained to the appropriate standard. Generally, for aircraft with multiple decks, this means behind the load as the crash restraint usually is comparatively low. For smaller aircraft, where the crew is the meat in the sandwich, the load will be restrained appropriately so there is no problem putting seats in front .. caveat .. the clearance between seats and (typically) net has to be sufficient to allow for restraint deformation under crash loads so that the folk in front have some chance of survival.
In an earlier life I spent lots of time flying QC F27 and B727-100/-200 with palletised seating ... and, likewise, B727 with a load restraining bulkhead having seats ahead.