The TV I'm looking at (Sony X900E, or gulp, X940E) are LED and can get far brighter than the Vizio M-series, and have deeper blacks as they use local dimming. OLEDs don't get as bright but NOTHING gets as dark as an OLED so the split (contrast, the whole point of HDR) is often as good or better than LED however. TVs out there aren't 12 bit like you said but they also don't have the ability to cover the full contrast split that Dolby Vision supports today, that will of course change in time.
HDR10+ may help like you said but its not quite true that todays HDR10 tvs will be getting a full update, the full HDR10+ spec requires HDMI 2.1 which is coming to most tvs in 2018 and isn't present in 2017 models, so the updates (for example for Samsung which is hardcore HDR10) will allow HDR10+ via streaming sources only, you will never get HDR10+ content by cable, so no UHD Bluray support or future cable box support etc. For that you'll need a new tv.
