DISH doesn't need 148 slot any longer ,but they don't want anyone else to get it either. At one time 148 was in use for west coast folks ,but they haven't needed it for anything in years since they went with 129 sat.
I doubt they are even attempting "warehousing" as it is ILLEGAL and you DO NOT tell the FCC that you have very serious plans that after the sat for 61.5 goes up will "crystallize" long held plans that include DEFINITELY using 148, and then NOT implement them as you told the FCC you would. This could cause the FCC to DENY any future requests such as one similar for 148. Dish pretty much told the FCC that the only reason they are not using 148 today is because of satellite failures, one of them before the expected end of life. By that position, they are also saying (and clearly stated so) that when they do have enough sats in orbit--with the next launch and the Quetz sat capacity--they will absolutely use 148 as permanent use of 148 has been part of their plans all along and have pretty much promised that is the case when Quetz and 61.5 are settled. The FCC takes into account your actions on previous matters in consideration of your requests. Yes, as you said, Dish would not want anyone else to use it, but it is NOT a ConUS slot and right now NOBODY I can think of really wants that slot and Spectrum 3 (was that the name?) is pretty much dead, is it not? Wing sat slots just aren't very desirable nor economical for any startups. I think Dish really has plans for this, but they may be modest, just enough to not run afoul of the FCC or they really could have GRAND plans. Either way, they are going to use 148, unless the next sat launch fails.