Based on news I was hearing on RTHK, the SAR government may be lifting some of its social distancing rules within the coming month or so, but that the ban on foreign nationals is expected to be in place for quite a bit longer, at least on the order of a couple months. The guest on the show was also saying that some measures, such as wearing a surgical mask on public transport, will likely remain until a vaccine is widely available, so 1+ years from now.
But as to your actual question, if I had to guess I would say maybe the government would first do a partial opening possibly in July or August with a quarantine period for anyone entering HK. Then based on how that goes (and depending on if there is a resurgence of cases in the fall in cooler climate countries), they might reevaluate at the end of the summer.
If you are looking to make a "quick" trip into and then out of HK, I would say that might be a year or more off still. But just my two cents!
Anyone else have thoughts?