I would think this 10/20/100 chips per board thing is all up in the air until Avalon release the data. 

From what i can work out, Burnin's original design follows Avalon's own ASIC system (10 chips per board, 32 boards per system) - which is no doubt why he chose the design, as it's a fairly safe bet it's going to be straight forward to design and build. When you start adding X chips per board no doubt it gets tricky with controlling them and powering them, and you will enter into an unknown situation.  By doing 10 chips on 32 max, he's much more likely to have a working product and ship within the quickest possible time.

See https://en.bitcoin.it/wiki/Avalon  - (10 chips per board, 32 boards max in a system)