Someone asked about the speed. I measured with the Minimig AGA "newcpu" core 1.0,with SysInfo : CPU speed was on par with a 65 MHz 68030. (although the emulated CPU is a 020). It's better than what I had back in the days so I'm happy 
SysInfo's CPU performance measuring is a joke. The 68020 actually has more integer instructions than the 68030 although there is a good chance that CALLM and RTM are not even emulated in any FPGA CPU cores. The 68030 received an MMU (with instructions) which is mostly not used on the Amiga and a data cache. There is very little difference between a 68020 and 68030 on the Amiga as far as compatibility.
It is possible to reach 68040 and possibly even 68060 integer performance in an FPGA like the Mist or FPGA Arcade uses. Maximum performance is unlikely to be seen in these devices because the CPU cores are not that advanced and target maximum compatibility instead of performance.
In the long run, we can expect great stuff like Ethernet, RTG and AHI support. If those meet enough success and maybe if other developers jump in I guess 
Maybe if open standards and cooperation reduces the amount of work needed to bring these kinds of boards out. Informing the Amiga community about these products might help their success but seems to be a slow process.
Mist info and de facto forum:
http://harbaum.org/till/mist/index.shtmlhttp://www.atari-forum.com/viewforum.php?f=101FPGA Arcade info and forum:
http://www.fpgaarcade.com/replay/http://www.fpgaarcade.com/punbb/There are various threads on this site and others like EAB if searching for topics like the board names or FPGA. There are also various youtube videos.
