This is my $.02 as a current -135 AC, and a Coronet Detail Planner with one of the Guard TTF shops. I have about 6-7 years in the 135 and about 3 years now of traveling around the world as a Coronet Planner on KC-10s.
I'm not going to engage in any of the community/culture bashing or wenis measuring contests. Most tanker dudes are good pilots/booms and want to do their job well. Some suck, and want to keep sucking. No community is immune.
From a planning perspective, JarheadBoom hit the nail on the head. A safe rule of thumb in the coronet world is that 1 x KC-10 = 2 x KC-135s. As a planner, we obviously love to reduce the number of moving parts whenever possible. But could we do some of our most complex coronet mission sets (ie, Strikes from KMUO-AOR or 22's from PAED-AOR) with only 135s? Of course. We have done it, all the time. We have also done them with only KC-10s. In the end, the missions are completed with similar rates of MX issues, etc. What matters to the people who’s opinion matter is that the fighters get delivered nearly on time, not a 10-20% cost differential.
I have also seen it go both ways with receiver units. Some Navy/Marine units have squawked about 135s. Some got KC-10's. Some were told that the 135 was their only option. It mostly had to do with tail availability. I have yet to see a unit wait for a KC-10 to free up rather than deal with a 135 and go on time, especially when headed westbound. In the case of FMS sales, the rcvr units (most recently Tornados for me) get what they want for obvious reasons.
As others have said quite accurately, if big blue does cut the 10 it will be completely about $$. A smaller inventory (less than 20% of the 135 fleet size) with overlapping capabilities would seem to be an easy target. All semantics about who has more items of flair aside, we have other jets that can offload gas and move cargo in the inventory, and rcvr units will adapt. We as planners will adapt, but it will suck.
All that being said, I think this and discussions about chopping the A-10 are mostly posturing to wake politicians up to the impacts of sequestration. But anyone who convinces themselves that their job, airplane, base, etc, are indispensable in today's military is just setting themselves up for failure.
~NH