Actually now that I think about it, a Samurai Shodown/Last Blade crossover would be tight. IMO for it to be a successful crossover, both series has to have the same setting, and charcters have the same nature in their fighting styles to create chemistry.
Capcom vs. SNK was successful because they were both set in modern day...EVERYWHERE. Capcom and SNK characters had things in common:
>They fight with their hands and feet, some had weapons (Rolento, Billy Kane)
>They throw fire or any elemental attack in any shape or form
Samurai Shodown and Last Blade were both set in ancient/feudal Japan.
So as for series such as Guilty Gear, there is no match up for a crossover, since GG provides a straight up unique fantasy based atmosphere that no other fighter has done.