Why making a whole new bios? the idea is cool, but im sure you will not see this in any near futher at least thats what im thinking
reason is being able to keep the network share mapped while the game is running. Since you cannot have your own loader which will continue running while the game is loaded and being played on the psp you need to go a level lower to be able to run some code in the backgroun which will keep the network share attached to the psp - hence new bios, or at least this module integrated into existing bios. Otherwise only the game would start loading and psp would forget everything about the network share mappings, tcpip etc.