So far, all the new outdoor VHF/UHF antennas that I have seen that are available or have been announced (Antenna Craft, Channel Master, an Winegard) have been for channels 7-69, not 7-51. Why? They are for the most part just modified versions of the channel 2-69 versions. Eliminating channels 2 through 6 is easy with most of them (just eliminate some elements) and shorten the boom. It requires minimal design, testing and retooling work, and it makes the antenna smaller reducing manufacturing and shipping costs and improving curb appeal so more folks will be willing to put one on their house instead of relying on an indoor antenna. That change is a no-brainer. The UHF Yagi section of them could be redesigned for channels 14-51. But that will yield only a very small change in performance or size. There is very little motivation for a manufacturer to change the UHF Yagi section of an existing design in that case. Doing so requires real engineering: design, simulation, testing on the antenna range, and retooling, all of which costs money when the current design works just fine and the net change in manufacturing and shipping costs, and performance, will be minimal.
Will channel 7-51 designs dominate for totally new designs? Of course, 98% of the market is there. But, so far, there aren't any totally new designs because there isn't a compelling reason.
I am curious as to what benefits ota.dt.man expects from an antenna designed for channels 7-51 instead of 7-69. If it is significantly smaller size for equal performance for a given type of antenna, or significantly more gain for the same size and type antenna, it ain't gonna happen. It is basic physics. Yes, you can improve gain slightly when you reduce the bandwidth of a Yagi, but it won't be by a significant amount.