You can EASILY outfit a full medium house with 300 slots but only if you are doing a standardised non-glitch/non-combine style of house, ie just get stuff and put it down. Once you move into the glitching/combining level of building then yeah I can see my medium house running out of slots pretty quickly.

My larger beef is the outdoor limit but I don't see that changing due to server/shared space issues in the outside world.