HDR on iPhone 7, 7 Plus, and iPad Pro (Gen 1)?

Even though they don’t explicitly support HDR like the iPhone X / 8 / 8-Plus /iPad Pro (Gen-2), the previous generation of devices all FEATURE full P3 displays with support for wide color, and all have good contrast. Is infuse tuned to display HDR 10 on these previous generation displays, while at least keeping the wider color support they have?

If not, you should really consider a wide color feature (P3 vs sRGB) for displays that are not HDR tuned but are P3 displays. (In fact, this happens to be the case with the newer iPhone 8 and iPhone 8 plus, which have essentially the same contrast rating as the previous generation.

Yes, Infuse will display proper wide color (P3) on supported devices.