I personally like the idea of a new style of accelerator. Nowdays you can only buy 2nd hand accelerators and they might not work.
I don't think about a big gun like PPC or faster processors. I beleive the old Amiga systems must stay 68k based so a 68030, 68040 and 68060 based accelerator is a good idea.
The Natami project is very good , I like it but that is not our much loved old HW. I am sure I will buy one but beside that I will always have the A1200.
One of the main drawback of the A1200 is its 14Mhz local bus. You can design a fast accelerator but that will always have to talk to the motherboard using 14Mhz clock driven protocol. That is why if you make different tests with different accelerators the CHIP ram read and write time is nearly the same for all. An accelerator card itself is a small computer which is fast on its own board but access to outside (towards the A1200 motherboard) is slow.
This however doesn't mean that we have to give it up!
I started to think on a new design which is using FPGA for the main bus driver plus memory controller logic and have SIMM modules (or even DIMM SDRAM) as memory. CPU would be a 68030 040 or 060 but in order to make a twist on the design and create something new I would put 2 CPUs, a 68030 and a 68040/60 on it. During power on the system would startup with the fastest CPU but if you would hold down a key a menu would appear where you could choose between the onboard 020, the accelerator's 030 or 060 CPUs. Just like in WinUAE you set the CPU type. After you have chosen the system would reboot and startup with the chosen CPU.
One more important thing would be that if you would choose the motherboard's 68020 as CPU then you could have 8MB of Fast RAM from the accelerator card (even if you have a 128MB SIMM on it).
I beleive it is possible and even if this would not make money it would be a good experience to create it. I don't know whether it will ever come true but I started to investigate the hardware docs and how the Amiga bus system works. I will make some feasibility studies and develop some part of it (e.g. DRAM controller, A1200 motherboard local bus bridge). If any of you have good, unpublished or rare doc about the A1200's inside please share that with me!
Thanks