Vaishali Already Ek Extended Train Thi, Aur Barauni koi bada town nahi. Saharsa/Begusarai/Khagaria wale jaate the BJU ise board karne ke liye, To iska Extension inevitable tha.
Vikramshila ek fully Established City se originate hoti hai. BGP akele ise fill karne ki capacity rakhta hai, isliye iske extension ke chances almost nill/negligible hai.
But Yes, IR ke Recent trend ko dekhte hue anything is possible.