I'd agree with Target it is just an extension of the events filter, in fact you can do this on the map compare page already (set hidden date range, choose centre point/radius) and that is pretty fast.
Also the numbers of new caches each day aren't particularly big - in January this year it averaged just 83 per day in the UK, scaling that up worldwide is still going to be manageable, plus you could probably make some great savings by optimizing the case where a group of caches in a series are published (and so geographically co-located)