The soonest it would happen is the 2030s. I follow the NBA. There are currently 30 teams. Most around the Association believe that the next two franchises will be Seattle and Las Vegas, and afterwards the NBA will restructure from being 2 conferences of 15 teams to 4 conferences of 8 teams.
Vancouver could get in on the next expected expansion of 4 teams that'd stretch the league from 32 to 36. Mexico City might be in the running as well.
Upcoming TV deals are likely to influence Vancouver's odds of getting an NBA franchise. Currently, the largest TV deals are domestic US deals, like TNT, ESPN and NBC, and in these cases, Canadian viewers effectively don't count. More international and online TV deals for the league as a whole would probably increase the odds of more non-US teams in the NBA, like one in Vancouver.
Another factor is that Raptors owners, rogers and bell, are used to having basically no other competition in the Canadian telecomm and sports broadcast markets. I think that they would have the means and motivation to effectively block another NBA team from expanding into Canada.
The Vancouver Grizzlies were awesome :D