It would definitely be wonderful if 20-25 gpus could work in a single system.
However, this is not easy at all. There are various limits of gpu numbers coming from bios, OS, drivers, power delivery...
Check this thread for reference:
https://bitcointalk.org/index.php?topic=64450.0was sticking to 5 gpus per system, on the cheap base systems I have (gd45 mobos, 8gb ram) but the idea of turning that into 20-25 gpus per base unit would be very entertaining! (Not that I could find enough GPUs to fill it at this time)