They should deploy or forfeit the spectrum and pay a "spectrum squatting" penalty 2X the value of the spectrum. Those penalties go into a pool for loan guarantees for startups. Simple. No buying up spectrum and sitting on it for years. If you do, taxpayers through regulation make sure it isn't profitable.
Don't buy it unless you have plans to use it PROMPTLY. 2-3 years is enough to show deployment progress. "Intent" isn't going to cut it because the telcos like VZ and AT&T are a bunch of frakkin' liars and cheats who have made a business stealing from taxpayers.