I feel that neither product will want to go on BT YV as it currently stands. Both propositions have HDR and Dolby Vision as key selling points. If and when the 'New Box' appears and features these new video processing methods onboard then they'll consider the platform as compliant enough to carry their services.
BT when designing the new box will need to consider different output profiles for App and Catchup services. A standard output set for all will lead to differences across different outputs.
AppleTV does a decent job at equalising but also offers the facility for different apps to control what the box outputs with different parameters as specified for the material coming off the app.
Sounds cool. Do you know the timeframe on that ???
The last I heard was potentially an announcement this month and a launch early in 2020.
But it's all rumour and we all know that BT struggle to stick to timescales even when they make an official announcement!