I do not have all the data available to me(USAF retired 2008, former HQAMC and C-141/C-5 dude), but it seems to me that we are unlikely to replace all of the tankers 1-for-1 ... just too many tails. According to the current USAF fact sheet on the KC-135, there are 415 tails out there. So, while it would certainly be nice to replace all of those tails 1-for-1, is it reasonable to think that this will happen? Each tail might be cheaper than each tail for a bigger jet, but the logistics required for that many airplanes versus a smaller fleet of bigger airplanes is substantial.

Barring a 1-for-1 replacement, a 767 sized tanker (with significantly fewer tails) is probably the only option.

I suspect the DoD budget will be cut in the process of trying to "balance the budget", so it will be interesting what direction this goes. I suspect it will get worse before it gets better, and it may take a "wing off light", thus grounding the fleet and endangering national security, to get this problem fixed.

I hope I am wrong about that.