Well there was the Vampire 1 last year, I think the hardware is not the problem, it is the development of the fpga cpu.
One person in the world has developed two versions so far and you think hardware isn't the problem? There are far more people developing cores for minimig/mist/fpgaarcade and there are fpga cpu cores you can take off the shelf. It's easier and cheaper to get into HDL side, prototyping and designing boards is a whole different game.
It shouldn't be too hard to translate the A600 Vampire 2 into an A1000/A500 board, so I'd expect to see that next as it might sell a few. Maybe an A2000 board if someone is interested, but as it's going to be closed source then you will need to get someone in the inner sanctum interested as it will probably require a few tweaks. Probably won't sell many but the effort should be low.
An A3000/4000 card is going to be a lot of work as it's a much faster and more complex cpu slot, different buster revisions to deal with etc. The high cost of buying a few of them for R&D and potentially damaging them, compared to the low number of people who would buy one is likely to put them off.
A1200 is probably in between complexity wise and is probably the card that will sell the most. However the different revisions of motherboards are likely to create stability issues and they might want to avoid that altogether.
I am not sure what "Just to mention that this board will never enter serial production. It will be used only for development purpose. " means, but it might be that you need to wait for V3 to be able to buy one.
