Seems to me fleet planning at MON is a bloody mess. The high profile 787 order was quitely dumped, leaving the long term long haul programme up in the air, a huge question mark why the 787 was dropped, delays did not help but financial considerations may have been a factor in the cancellation. I too have never heard rumour of the 738 entering with MON, They are focused clearly on the 321 for their scheduled and charter but the 757s and A36 are still very important and useful for many Monarch high density short medium routes, clearly these two fleets are on the way out soon but what will they be replaced with, more 321s? I guess so but I think the 757 and the A300s, well there isnt a clear current production aircraft available from the manufacturers. I think a few new 767-300s before they stop being built would be a good idea. If MON ordered a few 763s, these would be good for the higher density routes that the older 757s and A306s serve.
I know the 763 is not a new type but they are still being built and airlines are still buying them new, and I think MON should think about a few new 7673s, they have experience of the type already, as they have used older ones already.
I think GIB will have to be 320, the 321 is too payload restricted for this route. The 757 was ideal for GIB when the demand was higher than the 320. the 321s are economical certainly, but they are under powered and range restricted. Charter routes to Turkey, Egypt well I dont think an all 321 will be a good ide Time will tell when those old faithful 757s are gone, so many routes will have to fall with them, I think.