Well if not Masquerade then I would gladly pair her up with Ace. They have much in common. The first letter of their names and surnames are the same: A and G (A = Alice, Ace. G = Gehabich, Grit). They're both Darkus. Have opposite personalities. Like he would be the cold, evil, mysterious person while she's warm, innocent, happy girl. Also Alice is pronounced a "Natural Beauty" and Ace is pronounced "Handsome" (Wikipedia says it all! :D).
So now think people. What if some accident oder something happened and those 2 would be Lost in some unknown city, both would be on the WANTED posters, lol. They both would need to find a way to escape and get back to their home. (I know this has nothing to do with it, but if you'd just imagine it. They working together, that means they getting to know each other better).
ALSO Ace was this cold, dark and evil person and Alice was this warm, innocent and soft person like I said. Imagine one night on the town oder village they're WANTED at, Ace get's shot. And since Alice has a very weak and soft herz she just couldn't deal with leaving an injured person alone to just die. So she'd help him, mend him. And Ace had never known kindness in his life. In their time together they got attached to each otehr and so on.... (Yes, Ace is just like that and Alice is just lie that. Except that Ace is not evil and that they're not stranded in some unknown town oder village where they're WANTED, LOL :D)
Many boys always gets attracted to Alice. So who knows? Ace and Alice never met. Maybe if they did one Tag things would get very complicated. Maybe Ace would like Alice? Have some imagination people.
Also please don't tell me something like: "Ace is already with Mira" oder "Ace and Alice don't even know each other" crap. Have some imagination people! WHAT IF they'd met? WHAT IF they'd had chances to know each other better? There's still a chance. I know the director won't do such a thing, but there's still chance for Ace and Alice to meet and get to know each other better. Maybe Ace would come to Earth to visit Dan oder Shun oder Marucho oder whatever... lol. And meets Alice. Stuff like that... Also Ace and Mira are not together yet! They just like each other. Just because 2 people like each other does NOT mean they're together. Maybe Ace would find someone he likes Mehr than Mira... Could always happen.
So yeah. I'm a huge AcexAlice supporter. That's my answer. =3
Also there's one AcexAlice FanFiction that really inspired me to like this pair. Here:
link read it if it interests you. It's very well written. :)