Yeah, that’s highly unlikely to happen at this point.
For whatever reasons, Garmin decided to stop allowing new entrants into the syncing inbound to Garmin Connect (ala Zwift, TrainerRoad, Tacx app). But that stop happened years ago, and others like FulGaz have been consistently denied. Roughly of course those timelines aligned to their purchase of Tacx and the Tacx app along with it.
Certainly, if a player like Peloton were to come along, I’m sure they’d make it happen. But I’d imagine MyWhoosh is very far down the totem pole of apps that Garmin would allow inbound sync to happen to, if they were to decide to open those gates again.
[And to be clear, this is only for inbound sync into Garmin Connect. Outbound sync is basically wide open to any entity that simply posts a privacy policy on an outward-facing website…even if that website is just one page.]