I hope some background stuff might be of interest.
The selection of the boom refuelling receptacle for the A model was under debate for some while, especially when the weight issues began to bite in 2003.
The boom receptacle added a couple of hundred pounds of weight, as it had to be made of heavy metals to withstand the pounding it can get. It also needed a hefty and fairly complex retractable ramp door system, and worst of all its location on the fuselage spine took up scarce fuel tank volume - I seem to remember a figure of around 400 pounds of fuel lost.
I know that there was a RAND study done at some stage that looked at the USAF's policy of having all its aircraft equipped for boom refuelling. I seem to remember that it concluded that a probe and drogue system made more sense for smaller tactical aircraft, offering faster refuels at multiple points from a single tanker, and better NATO interoperability. Booms would be retained for the larger aircraft (e.g. B-2, B-52, C-17).
Again working from memory, but I don't believe that the space on the A where a retractable probe ( as per B and C) would be installed has been used for anything else. The main challenges would probably be the routeing of the plumbing and reprogramming the fuel management software.
The C model certainly offers longer range than a C, but at the expense of a lot of additional airframe weight (tons of it) that has to be hauled around with no benefit. A fairly obvious future variant could involve putting a 'C' type wing (without fold) on to an 'A' airframe, without all the additional weight required for carrier ops. Again, my memory may be at fault, but I think that this option may have been looked at at some stage at Fort Worth. However, it was probably a 'US only' effort. Such an aircraft could have had an MTOW of around 80,000 pounds, with an unrefuelled range of around 900 to 1000 miles.
Hope this is of some interest, best regards as ever to those working out the fleet mix,
Engines