Because this model relies heavily on knowing the location of buildings to distinguish between outdoor and indoor signal loss, it may not be very practical for use on a nationwide cellular network. Keeping track of the large number of buildings for cities across the nation would result in a rather complicated model. It is also based more on experimental data rather than on a mathematical algorithm, and it would likely be difficult and expensive to obtain this data.
On the other hand, if using the model results in significantly better predicted coverage, then the cost of developing it for a nationwide network could be balanced by higher revenue. This would probably be a long-term result, however. Still, with today's advanced GPS and satellite imaging technology, an implementation of this model could be feasible.