What I’ve understood from @Quirk’s remark is that he’s talking about e.g. 480p50 - which isn’t a resolution supported by TVs/AVRs - not “only” being upscaled to 720p50, but to 1080p50. So, as soon as this feature supports native resolution output of these resolutions (which a UHD TV would support):
he would like to have all other resolution/framerate combinations upscaled to a 1080p output. And not to the next higher possible resolution (instead of e.g. 576p60 -> 720p60 he’d like 576p60 scaled to 1080p60 even if ‘Also allow resolution switch’ is enabled). So, all supported HDMI resolutions/framerates output natively and those not supported all scaled to a fixed resultion which is not necessarily the next higher supported one, but e.g. always 1080p.
I have to say, it sounds difficult to do… But it would be Sam’s part to evaluate, if this will be possible.