Given none of the three major US airlines allow lounge access on solely domestic itineraries to even their own Gold (or Gold-equivalent) members, I can understand why United isn't racing to offer such access to VA Gold members.
It's reasonably safe to assume that the Big 3 US carriers only begrudgingly allow Gold-equivalent members from other carriers within their alliance lounge access on domestic itineraries because the alliances' rules have effectively forced them to do so, not because they want to. Of course, selfishly, seeing VA join Star Alliance would still solve this problem for me as a VA Gold, not a United one.
I'm flying UA in October with my VA number rather than Star Gold as the trip will get me to VA Platinum and my Star status is set. There are 2 domestic sectors from ports with United Clubs, but as it's all one ticket from Sydney, I shouldn't have lounge issues, though I will report back with any updates.
Peripherally, +1 for Air Canada. They need to get something sorted. It feels a bit silly flying an airline to get SCs to maintain status, while sacrificing the benefits of said status to do so. I flew AC last week with my VA number but managed reasonable upgrades to J from PY on both sectors so didn't need get the Star Gold card out for any benefits. I wasn't particularly impressed with their J product, however, so won't be rushing to drop the cash again flying back. I read on a recent FlyerTalk forum for AC that some people input their Star Gold number when they first check-in online, and then modify it to another carrier to credit the flights as apparently AC's desktop (but not mobile) version of their online check-in will allow this. They've then reported successfully using the original boarding passes with the Star Gold benefits showing for priority screening and boarding, and showing their Star Gold card at lounges where the agents are likely to actually look at the reservation. This isn't against any published Star Alliance rules, so I don't have a problem with it, and may give it a go on my way back. Will report back on that as well.