Thanks a ton to everyone for your replies so far! It's been extremely illustrative for me. I will now try to clear up some of the finer details.
All controllers will use USB and there will be 4 USB ports ideally. This will allow for game controllers, keyboards, and mice.
I had huge plans for doing all kinds of computers on here as well. C64 is pretty much done- I have made an FPGA SID player! This includes 90% of the C64, because it runs every single SID file (yeah I tested all of them) and you have to run the BASIC ROMs and such. For "realSIDplay" files, it actually boots the C64 OS and waits for the blinking cursor before faking typing in SYS nnnn or RUN depending on which type it is (ASM or BASIC).
The FPGA SID I have done includes a real analog filter that closely models the real chip. The SID HDL code is 100% complete and fully debugged and even supports lots of the weird things people have come up with like high quality samples using the PWM, enveloper, and other weird crap. And it handled the "looped noise" effect as well. The only slight fly in the ointment is the filter is external analog hardware so I wouldn't be able to include this filter on my system.
Atari 5200 is notably missing because it's really a rebadged Atari 8 bit computer.
The mysterious lack of computers is due to my up until now lack of keyboard/mouse interfaces. I have great plans to add all sorts of computers. Emulating the floppy drives is also a big pain in the ass (especially the devil known as the 1541).
Some people have wondered how the actual game loading works. It works like this:
You dump a directory onto the SD card that I provide on my website, and then put ROMs and what not on it.
The FPGA bitstream ("program") is automatically pulled off the SD card and loaded into the FPGA to reconfigure it for the system you're attempting to run. It's all 100% automatic to the user and everything "just works" .
If I provide cartridge adapters, the adapter will automatically configure the system and pull the proper bitstream off the SD card to make it "just work".
I was going to support saving your saved games to SD card, and I am on the fence about save states- because this is "real" hardware, it makes doing save states quite difficult. I might provide it on some things but I can't guarantee it.
Re: do light guns work on 31KHz VGA scanline doubled video? In some cases it does! I modified my NES zapper gun to double its sense frequency from 15KHz to 31KHz, and duck hunt played OK though range seemed to be reduced some. I could probably increase this range but didn't try too hard. I wanted to see if it worked, and it did.
When I release new cores (or update old ones) all you'll have to do is drop the new stuff onto your SD card and plug it in and you're good to go. Speaking of new cores, these are my goals for the project:
SNES, Genesis, and Neogeo (and TG-16). I want to do other cores as well but I will feel like I accomplished something with those three. I also have a chubby to add super acan, believe it or not. I don't know why but it seems like an awesome challenge to me. I also own 3 of the damn things I paid 99 cents for :-)
I also want a huge galaxy of computers too. This new hardware I came up with is the key to getting all of these cores going.
tcdev: thanks a bunch for helping explain the wonders of FPGAs. I like your work :-)