While I'd rather they remain distinct, I think there are ways they could be combined. LevelUp combines Tiefling and Aasimar into a single Planetouched ancestry fairly successfully. I don't think this works nearly as well.
The main sticking point for me is a distinct lack of a "one neat trick" that you get for choosing the gnome branch. Dwarves and Elves get darkvision, along with their distinctive traits.
In my feedback I suggested "Keen Sense of Smell", giving advantage on Perception, Investigation, and Survival checks involving scent. However, I'd be fine with anything that could be called out as a gnome's unique thing.