Hmm
Iain Forsyth fairly well sums it up but misses out one detail. One of the questions being asked by OfCom is if they opted to sell off some spectrum for such uses then who would buy it ? As Iain points out, there is no 'big user' that would be in a position to bid for it - only lots and lots and lots of little users. Even if they managed to get together and raise a successful bid, there would be plenty of individuals who would decide to freeload and not chip in. Any form of 'per use' or 'per user' licencing scheme would be expensive and inefficient to administer (which is why several existing licence types have been made 'free' or 'for life' instead of annual for a modest fee.
Contrast this with uses such as mobile phones and related stuff. There you have a small number of large comapnies buying spectrum which they then rent out to large numbers of consumers. What allows them to control usage and get a return is the way that the consumers equipment doesn't work without the network - ie totally the opposite to the radio mike use.
So there are several problems :
1) The loss to the many small users faced overnight with redundant kit (which has no second hand value).
2) The cost to the same users of buying new (and therefore even more expensive) kit at a time when demand is good which keeps prices up !
3) The problems of running any form of licencing system which is unlikely to raise significant profit whilst being affordable.
If there is a mandatory change, then the only reasonable way to do it is to licence a new band/system and phase out the old over a significant period (not less than a decade). Over time many users will have switched to the new system thus lessening the problem. Such a changover could be accellerated by blocking the sale of new old equipment.
As for suggesting something like WiFi - all I can say is that a suggestion like that can only come from someone who a) doesn't have a clue about the technology, b) had never tried to use it in a 'busy' environment, and c) has no idea about the requirements for real time audio !