Two things are going to bite you with balde servers. Power and Cooling. It is typical to need a 10-15KVA UPS for a balde chassis, and the device will need on the order of 5-8 tons of cooling. Think of all the power and cooling a room with 8,10 or 16 servers would need, and squeeze that into a 6U form factor. Airflow must be deliberately managed in the cabinet, or around the chassis or you WILL have blade failures.
APC put out a nice white paper on delaing with blade servers. They are of course trying to sell their cabinets, but the facts are sound.