A recent study performed by the Royal Institute of Technology in Stockholm concludes that there are no benefits – at least before 2020 – in replacing terrestrial broadcasts with a cellular network capable of video-on-demand unless viewing habits change dramatically. Further only very small spectrum savings could be expected. The breaking point for cellular to be better than broadcast is estimated to occur when terrestrial broadcasting has less than 3% of viewers.
Read here an article from the MIT Technology Review about this and access the whole study here.