NWSRG:
In short, the received wisdom is that you can't convert a Tranche 1 aircraft to Tranche 2 standards, let alone Tranche 3.
The aircraft differs in a number of respects, not least in having an entirely different processing infrastructure, which means that Tranche 2 software can't be hosted.
It also could not be economically upgraded to hang a heavy AESA off the front bulkhead, nor does it have adequate electrical power and cooling.
The aircraft can be upgraded to address obsolescence issues, and with that done, could gain all main T2/T3 capabilities via further software drops.
I don't expect that will happen, however, and think it more likely that we'll see two extra squadrons, one at Lossie, one at Coningsby, which will be equipped with obsolescence-addressed T1 jets, used for QRA, A-A, and red air, perhaps with the austere A-G capability stripped away, and quite possibly with aircraft that are not deployed, except to the Falklands. These probably will have further improvements via new drops, but will not get all the P1E/P2E/P3E enhancements.