Yes you can go to Skardu via Naraan and Babusar top on motorbikes. The bikes should be in good condition and you should carry tool-kit and puncture-kit, carrying extra tubes or tyres provide more safety. There is no workshop between Naraan and Chilas.
The road has been under construction for a few years now. I came back from Skardu, Khunjerab trip through this route in June 2008 on my GS150. Pakistan Bikers Club's trip went to Northern areas via this route in 2009. That year there was a lot of snow and the road opened late. Last year there was some dispute between two departments, probably NHA and FWO, so the road was not opened till late. Just keep watching threads about this route in summer, you will know when the route opens up.