of course it would be easier to take up other musical instruments with G4 piano knowledge already, but i must say that only starting to learn the violin at 10yr old is a bit late already becausemost start at 5 or 6 yrs old so they have a head start and it will be hard for your kid to excel unless he is really talented.
perhaps learning some less popular instruments such as the horn, the oboe etc. will be more advantageous