>Cortex-M is a lovely platform. Shame it has stagnated.

Cortex-M is the Arm Inc. micro-controller (or MCU) profile, hence them M, so DDR3 or PCIe are out of scope here. You also only run thumb code on the M profile.

edit: Did you mean STM32 Nucleo, the line of MCU dev boards from ST?

> Otherwise using those platforms is a bit like programming on 8086 today. Fun. You get basic stuff done and then you hit a wall.

If these platforms are as problematic as you claim then they would not sell as well as they do. The problem is not the platform but how you are using it.

> Only option is to jump on SoM stuff or FPGA which is another can of worms in itself.

Only? For what application? SoM means system on module and is nothing more than a ready to run CPU board you plug into your circuit board. Do you mean an applications CPU running a general purpose OS like Linux? And an FPGA is a completely different animal. Normally an FPGA is needed when you need specific custom logic to accomplish a task OR interfacing hardware with glue logic. Otherwise programming an FPGA is way more difficult than an MCU.