I don't think 2 ways extention at the same time is possible. Originally avdha assam exp was from Lucknow to Guwahati then it became Delhi-Guwahati, Lalgarh-Guwahti, Lalgarh- New Tinsukia and finally Lalgarh- Dibrugarh.
I think extension of JP-INDB upto FZR is feasible only after changing the running days as lie over on Sunday is not sufficient. Delinking from JP-PUNE is not a major concern if RB provides new rake.