Once a railway station climbs up to NSG1, it's rare that it'll fall back to NSG2. I think Gorakhpur will stay as NSG1 even if some trains get shifted to other terminal stations of Gorakhpur.
At most, what will happen is Varanasi (BSB) will overtake Gorakhpur (GKP) as most revenue maker station of Uttar Pradesh, since soo many VBs are getting introduced from BSB and i heard both of the BSB - NDLS VBs will become 20 Coacher. These things will only push revenue up for BSB in coming future.