Can bi-ritual priests become bishops?
The short answer
Yes. The Holy See can appoint any priest as bishop for any rite, though ordinarily a bishop is appointed for the rite he has always belonged to. Bi-ritual priests have permission to celebrate in more than one rite but themselves belong to only one.
The Holy See's choice
The Holy See can appoint any priest it wishes as bishop, for any rite. Ordinarily it appoints a bishop for the rite to which he has always belonged.
What "bi-ritual" means
Bi-ritual priests have been given permission to celebrate the liturgy in more than one rite. The priests themselves belong to only one rite.