As outlined previously, I am in full agreement with those who opine that any major rebuild investment at MAN is 'off the table' for the foreseeable. My guess is that the T1/T3 complex will serve another twenty years at least in a very recognisable form.
My proposals are for changes which go only slightly beyond essential buildings care and maintenance in terms of overall costs. T1 and T3 are already physically linked together. The T2 TP (we were told) will offer capability for handling domestic flights. So let's move them over there - far better for interlining business anyway. This opens the way for T1 and T3 to be linked together as one facility airside very easily. The link corridor between the two (Southern Front) is already in place, but as a domestic facility must be kept sterile from international passengers. Once that need is removed, it is pretty much just a case of shifting afew barriers and opening doors. No major rebuild required for this particular task.
If I'm right that the T1 car park must come down anyway (life-expired structure) that leaves a large space available adjacent to the existing T1 entrance foyer. My suggestion here is for a cheap extension to accommodate more self check-in kiosks and baggage drops for departures and egates / baggage carousels for arrivals channels. Many will recall the "temporary bussing lounge" which was attached to the T2 structure during the TP extension build-out. This structure was (relatively) cheap to provide, but it was undercover, functional and adequate for the job it was intended for. An extension of this kind for the purposes described above is entirely 'doable' on a tight budget and sufficient for the needs of no-frills carriers. It also introduces the opportunity for operational cost savings, as if it provides sufficient passenger processing capacity it removes the need for the duplicated facilities currently serving standalone T3. Open up that former domestic corridor and all passengers could be processed through the T1 channels to the combined airside gates.
T1/T3 do feature a number of widebody-capable stands. I suspect that most of these are already marked out with L/R centrelines to accommodate two smaller types, but if T1/T3 were to become an overwhelmingly A320/B737 facility, stand layout could be optimised without need for large-scale investment. My post some days ago in which I suggested lobbying Sunak for a handout from the £4Bn regional infrastructure fund was made somewhat tongue-in-cheek, but - HEY - why not ask the question? There is nothing to lose by putting in an application. Those extra few parking stands would certainly be useful to have, though I personally don't hold out much hope for seeing them in the short-term.
But my suggestion to combine T1/T3 and to build an inexpensive foyer extension on the old car park footprint ought to be easily affordable. And perhaps removing the need for duplicated security and immigration formalities in T3 could repay the cost anyway.
I do think it is fair to presume that major terminal redevelopment is a goner for years to come post-covid. So cheap but practical changes plus some essential maintenance are the way things will need to go. Fortunately, no-frills carriers love that 'bus station' look!