Yeah, Selwyn is kinda potluck opening weekend. It is pretty rare for them to have any decent coverage at that stage. As for their snow making ability, they are getting better and better, but they really do need the help of some natural falls to kick off their season. You are safer betting on a Selwyn trip from mid-July through August, unless you live close-ish and can just drive down whenever like I tend to.
I ended up there a few times a year with my 7 & 8 yr old girls as it's just easier and they don't get to ski often (Live on the Gold Coast with my Ex) enough yet to keep their skill level up. I have been lucky the last few years and ended up their after\during decent falls and have enjoyed myself enough, especially once my girls come out of their morning lesson and I get to spend my afternoon laughing with them as they repeat their ski-stack-giggle-stack-giggle-ski...... process.