Probably because of the super huge errata list?Or the lack of interest in complicating the software or the team simply doesnt still have lots of code for Xmega to copy to make a super duper core, like they made with the atmega....
There were also the initial availability problems. Xmegas were announced, but you couldn't actually buy them anywhere.And the "not 5v" issues.I have a partially complete xmega arduino design. I'm not quite sure what it is good for, other than running twice as fast as a normal arduino (which may be a problem in itself. The Maple and chipKit designs went to 4-layer PCBs...)
A lot of Sensors on existing shields only work with 3.3 V and also for example
It is not just twice as fast.It is also DMA, Event System, several UARTS, I2C and SPI interfaces.
bare metal programming ... means no Arduino silly things
so why need to use the Arduino IDE?
At this point, I'm sorta hoping that the chipKit (pic32 based) boards explore some of these issues.They have more dedicated support...
Yes I know that, but he wants to do low level programming that Arduino style will simply not deliver so why need to use the Arduino IDE?