@Neven
As a temporary measure, when playing TV with stereo audio, you should be able to shift some of the playing audio to the rear surrounds by moving the ‘TV Level’ slider bar to +15 in the surround settings of your HT product.
Quite the oposite, I don’t want to crank up the fake surround when listening to stereo source on my TV,
Also if you switch off trueplay temporarily you should be able to select a distance for the surrounds from the listening position.. set them to greater than 3m/10ft, as that too will add to the surround output.
I just want to add that I too did want to see ‘Full’ audio for TV stereo audio, as I like the added separation when listening to Music (Deezer) and Video (YouTube) Apps on my TV, but I suspect these Apps may eventually go onto support Dolby Digital Plus Atmos audio eventually, plus there are now devices on the market, like Nvidia Shield TV, that have these Apps and allow for upmixing stereo to 5.1 surround audio - so I’m not so sure that Sonos need to add this to their own speakers, but I certainly understand the reasons for your suggestion here.