Did you see the design specs somewhere ?
I wish, that's why I used the quotes

I decided to just go my own way for the time being. It won't be physically compatible and maybe not even electrically compatible but I hope to have it compatible with the tool chain. Like the rest of us though I have to wait and see.
Even a short list of features.
• SAM3U 96MHz ARM Cortex-M3 processor.
• A 72-pin backplane with 8 addressable daughter boards.
• Ability to individually reset daughter boards.
• 48-pin connector for memory expansion, fast IO and debugging.
• Three interrupt lines allow stackables to provide vectored interrupts to the CPU.
• Software control of power to the system and external devices.
• 512k bytes of external SRAM (expandable to 16.5Mb).
• Battery backup for SRAM and the SAM3U’s RTC/RTT.
• Serial PROM for non-volatile system parameters.
• High-speed microSD interface.
• Serial Synchronous Controller I2S interface for CODECs, DACs etc.
• External watch dog and power monitor chip.
• Eight 15v-tolerant analogue inputs.
• 32 digital IO with 5v or 3.3v support in both directions.
• 16 high-current digital IO with 5v or 3.3v support in both directions.
The schematics are nearly done, here's a render of a rough PCB layout.

I probably won't commit to anything until I see the real thing, it depends on how long that will be. Also I'm still leaning about the SAM and may make changes as I get to know more about the chip.
I have asked for input with little response but am still open to ideas.
I guess I'm, saying that I don't think an ARM Arduino will be a dud and I'm putting my time (but not any money yet

) into it, it's a logical extension to the Mega. As for the Due itself we have no details so that remains to be seen however just being part of the Aduino fraternity will help a lot.
On some other forum I also saw some link to 4x4cm cubish stacks with 32-bits from ... Atmel by a German startup. Maybe you could be interested...
Very much so, if you can find it please post a link.
______
Rob