I'm suggesting rec.709 because it's what is a currently expected default for a screen. In your typical setup, your working color space is something like ACEScct or DWG, so you can map to several possible output formats with a little extra work if needed.
The integer values are nice because existing video formats encode things as integers. So we can just stuff our stuff inside a codec we already have rather than having to reinvent the wheel on the codec side as well. Re-purposing existing toolchains for new uses tend to a thing that gets a lot of traction compared to building a new one from scratch. Even if the newly built toolchain is far better.
Aren't most phone screens "HDR" these days, and for years now ? (And Apple had wide gamut with excellent OS compatibility on computers for even longer ?)
Yes, but why existing formats are like this, we have been through quite a lot of new especially video formats in recent years...
The integer values are nice because existing video formats encode things as integers. So we can just stuff our stuff inside a codec we already have rather than having to reinvent the wheel on the codec side as well. Re-purposing existing toolchains for new uses tend to a thing that gets a lot of traction compared to building a new one from scratch. Even if the newly built toolchain is far better.