ten thousands of 6809E CPU would be a totally awesome architecture
interconnect would have to be thought out carefully
A 6809E CPU is about 9000 transistors. 10000 of them would still be 90 millions of transistors, while modern x86 are now in the billions range.
More problematic would be the RAM. If you have many cores, you need to give each core a few kilobytes of private RAM, at least for storing the instructions for that core.
Each bit of RAM is 6 transistors (unless you find a way to cram DRAM in a CMOS chip, which is what IBM does with the Cell CPU; it seems to be doable but hard, and patented).
A 6809E with 8 kB of static RAM means half a million transistors or so.
At that point, you'd better put a 32-bit 68000 or ARM core, it won't change things much
and 10000 cores with RAM would need 4 billions of transistors, which is in the range of the industrially doable.
Things are cheaper id the cores run in SIMD mode (many cores using the exact same instructions, synchronously). You need much less per-core RAM. At that point, you have a GPU.
And GPU do exist. I have a few of them at home.
3
Programming for SIMD is a bit hard, though.
