The FCC hasn't set a date by which all low power TV stations must stop broadcasting in analog, but it is taking steps to limit the number of new analog low power stations.
An FCC Public Notice (DA 10-496) released late last week stated that "In furtherance of the digital television transition, the Media Bureau announced that applicants for new analog low power television and TV translator stations must submit an amendment to their pending applications to specify digital operations by May 24, 2010."
The Public Notice includes a list of all pending applications. Changing emission from analog to digital is considered a major change and the applicants will need to pay a $705 filing fee for the amendment. Simply changing the emission type from analog to digital and reducing power to stay within the FCC limits for low power DTV (15 kW at UHF) is not enough. The digital interference ratios are very different from those for analog. Amended applications will require new interference studies. If there is a nearby co-channel DTV station, applicants may need to find a new channel or greatly reduce power.
I wouldn't be surprised if the combination of the filing fee and the cost of running new interference studies and possibly changing channels could cause some of the applicants to withdraw their applications or simply do nothing and let the FCC return the application. Considering the National Broadband Plan recommends reallocation of UHF broadcast spectrum to wireless broadband services, this may not be an unintended consequence.
