105 karma · joined October 29, 2015
As I see it, the ARM instruction sets (note the use of plural) are a moving target (look at Cortex chips with Thumb2 only). They are far from RISC if you count them, and the instruction encoding is horrendulous.
It's like saying "why not target Windows? I doubt that's going anywhere soon"
With FPGAs, your only risk is that the manufacturer discontinues the chip you targeted, and you can then target another brand with the same (or nearly the same) HDL code.
Another approach is to blackbox USB and HDMI, and consider them outside the project, much like the VGA monitor or whatever is in the keyboard to send PS/2 signals. You can connect to spare IOs on the FPGA board with 'blackbox' hardware, as long as protocols are simple and open.
There are hundreds of FPGA boards that do not meet the requirements of Project Oberon, in addition to the board you mention.
It is unique in its ability to boot Oberon in 1 second, straight out of the box.