It should be fast enough, as was demonstrated with some gCn programs, I believe. I think though, that for it to be fast enough you'd have to have both calcs basically only getting basic information from each other and each calc basically calculating everything needed for their game. (In a sense, the opposite of one calc being host, where one calc calculates everything and sends relevant data to the others)

Though I personally know very little about linking so I could be very, very wrong.

Edit: Reading what I have written, I say "basic[ally]" a lot

That would definitely be a good idea to have the single and multiplayer separate. Just for the program actually executing and sending data across the link cable it would have to send as little data as possible and still be able to work. So basically you could just have it send what's being pressed by the user in certain intervals and the other calc uses that data to control the corresponding character. That way one calc doesn't have to send all the data to client calcs which could be too much to send. The only issue would be if there's any disparity with randomized functions.

Imo, it'd have to be 8 way movement, And perhaps a Standard and Special attack. The SSB Formula could work well.

I don't think you'd even have to send that info. Basically I think you could get away with just sending what's being pressed and the other calc would control that character on its process with those key presses as though they're playing on the same calc. The only issue could come from if there's either differences in timing, lag, or random number generation. Or at least that's how I'm seeing it.

Lets see:
Possible-yes
Axe- not sure.
Grayscale: probably not with linking.
Nspire compatibility: Sure, as long as it doesn't use any incompatible commands.

Such game would be nice. For odd reasons, all SSB projects that got started in the past died, so as a result, there are no existing SSB clone for calcs. There's one Mortal Kombat game from me, but it's single player and uses ASCII graphics in TI-BASIC (not to mention the code was written back in early 2002 so it's very unoptimized).

Oh right I forgot about that one. It wasn't finished, though, right?

Also it would be nice if a MK clone had actual floors and background images.

I can't recall, it's been probably 5 years since I played it. I remember it being at least playable and fun, though. A background might get a bit confusing on the screen, heh.

As far as boot's question goes, you should be able to at least get a black and white version done. For linking, I'd say that HOMER's idea was decent.