In the particular case of MSHxSF, I'm still haunted by memories harking back to the olden days of printed media, of a report listing the secret characters and I was pretty hyped for Mephisto. What the report forgot to mention is that it was a red Blackheart... -_-"
As for Fukua, she's Skullgirls' Shen Long with some mythology behind it and with that in mind, I accept her. However, that is where I draw the line. Even with the small roster, I'm not in favor of expanding it by "Frankensteining" everyone in the cast and Skullgirls ends up like a 2D Plasma Sword. IMHO this sort of thing, in principle, cheapens the overall presentation as the character's animation is clearly not on the same level as the rest of the cast.
With some polishing - a few frames here and there to make her look less choppy and hopefully unique voice - she can become a worthy addition.
Overall, like many said, this has left me looking forward to Robo-Fortune even more.