Conclusion.

They may be lovers in the future. Or maybe not.

After going through the previous pages of the Possibility subsection, I think we can put it this way: We have several evidences both on manga and off-manga that can boost up the chance of Allen and Lenalee coming out as a couple. However, there are also things to keep in mind which might decrease that chance. That, being:

Regarding whether Allen or Lenalee will be paired up with someone by the end of the story... I think it's very possible. When Hoshino was asked in the Omake, "What is love?" She answered that she hoped to include it in the manga. I think some parts of her answer has been told, in Krory and Eliade's case. The love aspect was very deep in that arc. But I think it will be shown furthermore if it comes to the respective main protagonist! In my opinion anyway, haha. But well... I don't think the kind of love that will happen in D.Gray-man would be the one where one finally confesses to another then they date and get married and they live happily ever after... Nope. We're not talking about a shoujo manga. I think it would be more like... something that doesn't exactly say the word "l.o.v.e" but we can tell by the looks. In any case, all we have to do is to wait and see. And if you are a member of the Allen/Lenalee shippers: don't forget to keep our hopes up. Afterall, there are signs of possibilities we can't just ignore!