"Use it or lose it"
Is an excellent policy. Here in the states, for analog on 800mhz, since it was designed after Bell was broken up, one band was for the wireline company and the other for an independent. Once auctions and sales began, the FCC put a buildout date on the licenses, if some percentage of population is not covered by the date, the license reverted to the FCC. The first 1900mhz auctions did this too. It worked pretty well, where I live I've got 3 out of 4 national carriers to choose from and 2 local cell phone carriers (plus all the MVNOs). The later licenses did not have the buildout requirement, but there've been loads of sales from one carrier to another anyway. Carriers might want to sit on spectrum to harm the competition, but inevitably find another carrier's offer too lucrative and sell. A second part of this is "disaggregation", carriers here have for instance split a 15mhz (paired) license into 3 5mhz slices, selling each one seperately.
Anyway... I am concerned by TV spectrum being taken away as well. Here, a few cell cos that have worked hard on network tuning, they say there's no spectrum crunch (Verizon is of this opinion.) Some others (AT&T among them) say they need tons more spectrum, they want to cut yet more channels out of the TV band and sell them off. The 700mhz spectrum sale here sold 52-68 (and so 2-51 is still plenty of channels to avoid interference) but selling off another large block and it'd be difficult to avoid serious problems with cochannel interference.