They're pushing for a new park in Potomac, right? Why not just make it a AAA ballpark and put it there. Easier to find a location for a lower level affiliate than a higher one.
They'd almost certainly need to buy an existing AAA franchise to do that, and it's not clear that any are available (especially if the new owner planned to move the franchise out of town). Also, the P-Nats are themselves for sale and PW County has proven pretty stubborn as to funding even an A-ball stadium, let alone AAA. AAA stadiums are serious business these days, and all indications are that the last MLB team to buy and move a AAA club near its MLB city (Braves, Gwinnett County, move from Richmond) has gone very badly: the team was last in the league in attendance, with the next-lowest team drawing 50% more than it did. Serves the Barves right.
My understanding - might be wrong here - is that nobody is interested in Vegas due to the pitching environment and tries hard to not be "that" team stuck there.
Mine too, but it might trump being 2 time zones away. Another problem with Oakland as a choice, though: I doubt Oakland fans at large would be happy for any further association with Las Vegas than necessary, given the Raiders situation.