After having to meet some technical requirements, ATMega on current Arduino platform was not sufficient.
After some investigation I decided to get into ARM instead : -)..
I have started an Xduino project at www.xduino.com
to be able to extend Arduino platform beyond its current hardware limitation (not just ARM, perhaps PIC and other MCU will also be there in the future).
The first release v0.1(today) is for ARM Cortex-M3 72MHz 32-bit mcu plenty of RAM and flash memory depending on your actual board. I am running on STM32F103ret6 which has 512kb of flash and 64kb of RAM, >40 GPIO pins, ADC, DAC, USB, SPI, I2C, CAN, etc etc... lots of features. The price I got the board is pretty much the same price as my normal Arduino board.
The current syntax is not the same as Arduino, as balance between syntax and extended power of the mcu has to be considered. I am considering writing 2 sets of syntax, one for Arduino compatibility and the other as extended language.
If you get to try this please let me know. Also contributions are more than welcome.