There is a short section (unofficially) opened between Plains and Caldercruix. A very nice surface, sadly already graffitied. There are some sections laid, but entrance/exits aren't finished. No sign of any path between Clarkston and Plains at all. I was at Blackridge on Monday and you can see some parts are complete, but you cannot access them. Overall it's unfinished and if the station situation is anything to go by, probably well behind schedule.
You should also note that a new school is being built in Airdrie, on the current site of route 75 at Gartlea. I imagine diversions will also be in place there.