Originally Posted by matthey
Special purpose usually means a special price too. High end FPGAs are getting specialized hardware but they are expensive. IMO, creating an ASIC and selling cheap hardware makes more sense. A million dollars may sound expensive to individuals but designing and manufacturers boards like the Tabor probably costs hundreds of thousands already.
Well it would be an ASIC so there are extra costs. But it wouldn't be a replacement for a standard FPGA, it could be made much smaller and more efficient for CPU implementations.
The advantage for doing something like that would be increasing the potential market. Making a new microcontroller platform is simply useless - there are all kinds of variants out there from low to high cost and making something similar would take many years and/or a lot of licences for building blocks (memory, I/O etc.).
In comparison the CPU-FPGA would be useful for software->hardware translations, processor experimenters, university courses in computing science and even (if the costs can be made low enough) for retrocomputing enthusiasts. I'd assume such a chip would have a hardware memory controller, general purpose I/O (low speed) and PCIe connections. If one need more I/O standard support it could be done in external FPGA chip(s).
And there are many ways one could improve performance for making a processor in such a chip.