My reasons why CroMa is more possible than SoMa:
-Maka, as we all know, is a tomboy. Plus, she hates manly men thanks to her ftaher and idea of dating and falling in love to her is alien. Crona is everything but manly, and even though I think that Crona is a guy, I'll admit he does seem girly. He can be Yin to Maka's Yang on girly-manly level.
-Crona, who was never touched out of love, was hugged by Maka more hen once, understood by her and cared by her. All of this must've cause at least some kind of attraction towards her.
-Crona jumped in front of her and took a arrow in his stomach for her. She lost her sanity for a minute after that. That says a lot.
-Soul as her partener, handsome devil and cool guy he is, would be obvious choice as her boyfriend, but that's the thing. Too obvious. I really doubt producers would want the big question 'who is main couple' to be answered right on the begginning.
-CroMa has way more moments then SoMa, and Soul is never apart from Maka for long time so that has to mean something.
-Cromazoid as a name for the CroMa fandom supporter sounds really cool.