I don't think a fire-based Zangetsu is going to happen, as I don't think Kubo would change the function of Zangetsu that radically. It may be a true Zanpakuto now, but as Ichigo still is able to use Getsuga, and the larger of his blades is, for all intents and purposes, the same as his previous Shikai, I don't think the basic abilities and types are going to change.
As for the poll above, I think the idea that Tensa Zangetsu suddenly becomes a bow is laughable. If Ichigo were to sudddenly have to change his fighting style to accommodate a weapon he has no extensive history with and probably no desire to train with, then Ywatch might as well have won before they even fight. I think that, as Ichigo identifies more as a Shinigami than a Quincy, using a bow is not in his nature in the slightest. Also, there are Quincies who use swords, namely Yhwach and Gerard. Though, they may not strictly count as Quincies, as Yhwach is the son of the Soul King and Gerard is the heart of the Soul King.
My point is that it's unlikely, if there's even a remote chance, of Zangetsu changing into a fire-type Zanpakuto, and there's almost no chance of it becoming a bow in Bankai. For the first, the only connections we've seen between Engetsu (Isshin's sword) and Zangetsu are the names, Isshin's ability to use Getsuga Tenshou, and the fact that they are the Zanpakuto of father and son. As for the second, there's no reason for Ichigo to need a new ranged attack, especially after he now has Getsuga Jujisho. A bow would throw off his entire fighting style, and leave him without the advantages of the original Tensa Zangetsu.
