I don't think NER Will extend GTNR-GKP express till STP..It is daily express train and so much useful for daily passengers .. You are right that may be NER can use its rake between ASH-STP but not for 86Km.. Later on when from 2020 or 2021 till PBE track will be ready then only ner will introduce new express trains. Till ASH-STP or MLN only passenger train will be running..And if we talk about commencement on ASH-STP section then when track will be connected at STP then only train can reach upto STP but no official announcement yet for megablock.. If NER along with RVNL completes all the blocks for connecting tracks in September or first week of October then only train commencement is possible in December else we have to wait for long time i.e Feb or March 2019 for sure