VRR would be the most important feature if true. Handheld mode could use the overhead grace of allowing the FPS to drop as low as 48 on a 60fps game without needing to aggressively scale the resolution to always keep it above 60. For Nintendo games that will trend toward a 60hz refresh if the hardware can afford it, this would be a big fucking deal.
120hz is great in theory, but in practice would only be useful for enabling a 40fps option in handheld. But if you're running a game in 40fps mode in handheld and then you dock it to the TV, the game would need to be able to switch on-the-fly to 30 or 60, as they can't count on your TV supporting 120hz too.