I used to think the chimney concept for cases was the best one until I forgot about the dust filter on the bottom. Out of sight out of mind and oh my god was it a dust magnet. Its still a good idea to get the coldest air from the floor but it should come from the sides or front/back where if any dust cloggin occurs youll see it.
I like the mobo orientation tho with all the connectivity on top. It makes for a challenge to make the cable management not sully the case but its doable.