If there becomes enough demand simultaneous keypresses supported meny become a standard stat avaiable, but it is not likely.
I have heard that the SteelSeries Zboard h t t p://www.steelseries.com/us/products/keyboards/zboard/information supports many (7 I think) kepresses. another I have heard is Avant stellar h t t p ://www.cvtinc.com/products/keyboards/stellar.htm. Here is a link you many be intreasted in http://ask.metafilter.com/51940/Whats-a-brand-of-keyboard-that-allow-multiple-keys-to-be-pressed .