And 6 months from now, a transformer blows up in your neighborhood and fries your receivers, or a car crashes into a pole, or a lightning strike; whatever. DirecTV happily sends you replacements: an H23 and an HR23, which are the current receivers at the time. Both use wideband tuners and no BBCs, meaning there is satellite data on the same frequencies your OTA signals use now. At that point, diplexing is no longer possible.
Just something to keep in mind.
I'm certainly aware of that, but I'm also sure that I can cross that bridge when I come to it. Pulling another coax won't be any more difficult then than it is now.