[mhh__]

1. I'm not sure what you mean but remember that FPGAs don't run programs as per se (HDL gets compiled to logic, not instructions). The bitstream can be modified, it just gets loaded from some flash. I'm not sure where it's done, but it's possible.

2. The obstacles are billions and billions of R&D (and you'd need similar amounts to get a fab pick up the phone too). Reverse engineering the bitstream is also difficult because of this - Symbiflow (i.e. Trellis etc.) have got the bulk of the bitstream done (apart from specialized blocks like those for DSP), but you need to have good algorithms to decide what to do with that bitstream e.g. a fully open source flow requires intricate timing analysis.

[amelius]

Regarding 2: the question was about an open-source solution, so I think that "billions and billions of R&D" will translate to just a lot of time spent and no literal cost, e.g. just like GCC is free as in beer.

It is true that getting a wafer fabricated will cost a lot of money (in the millions maybe?) but this may be money well spent because the resulting FPGA design can be used over and over. I think this would be in the reach of perhaps some universities or government technology centers, if someone could formulate the case for it.

[mhh__]

Nearly all the cool stuff in GCC and LLVM is paid for by companies (paying the salaries of developers). The software could definitely be done in this way (Symbiflow is very very nice), but keep in mind that developing an FPGA will require a lot of hardware and bums in seats.

The question is similar in scale to building an open source Intel core i7 - it's not impossible but keep in mind that an FPGA big enough (for example) to prototype any subsections of the CPU let alone the whole thing would cost hundreds of thousands.