It will almost assuredly be many, many years before the government mandates a new OTA broadcast standard (if ever). The major movie studios aren't going to adopt a new disk format to replace Blu-ray anytime close to soon either (again, if ever). The major studios aren't likely to start shooting at 60fps commonly in the foreseeable future either (major motion picture movies will continue to be 24fps productions for a long time to come). There's just no major dynamic on the horizon to stimulate widespread demand for television sets with higher than 1920x1080 resolution (or even significant demand for content at any new framerates).

When content delivery over IP becomes a major avenue of distribution for the television networks and major movie studios, AND internet connection speeds exceed 25mbps (or so) in the vast majority of homes, then we might begin to have dynamics to stimulate some demand for living room displays with greater resolutions than 1920x1080. Even then, the growth of that demand is likely to be quite slow (likely to be even slower than the growth of demand for HD televisions has been the past several years). At comfortable viewing distances for living room video display, there just won't be that much perceptible difference between viewing 1080p and any higher resolution material.

This is why it's so important to distinguish between transmission and acquisition.

And as I said before, even if 1080p/50 never got transmitted as much, it still becomes valuable because it downconverts extremely well to any other 50fps format - 1080i/25, 720p/50, or 576i/25 for that matter.

Which is why the EBU are extremely keen for it to be adopted as a common ACQUISITION and interchange format within Europe as soon as practicable. It's widespead use would mean that neither 1080i or 720p broadcasters would be disadvantaged when material is interchanged - it would downconvert perfectly to either, as if their native format had been originated in the first instance.

Don't take my word for it - look at the EBUs website, EBU Technical Review , click "HDTV", and for starters look at item 308 - "HDTV — EBU format comparisons at IBC 2006". Even over two years ago, they were saying:
Hence, as regards the original question of this thread, 720p is likely to die out relatively quickly as far as cameras are concerned (as soon as 1080p/50 becomes mainstream) - or at least become a distinct second best, but be important for a lot longer as a transmission format.

In a way, it's sort of to bad that the US government mandated the switch to digital television when it did, and essentially set the standards for HDTV resolutions. At the time, the standards made sense, given the technology at the time. If the move to digital television had been delayed and the standards set today, we could have had just one 1080p60 (p50 in PAL land) standard. Microprocessors technology has advanced enough and AVC is mature enough now, that it would be quite feasible to implement (certainly as feasible as MPEG-2 720p60 and 1080i60 at the time the standards were set).