I'm actually really looking forward to the game - it shows a lot of faith in the franchise on Disney's part, to be making a separate game for it. If they're willing to do that, it makes it more likely they'd be willing to put figures into DI in the future. I'm with the suggestion of waiting until the next poll - Avalanche are getting figure requests
constantly and they're obviously focused on 2.0 at the moment, but when the poll is running is when they're making an 'official' note of requests. When the poll comes around again (as I assume it will), that's a really good time to launch a Twitter campaign and get people voting for Mabel and Dipper. Also, if you're able to, vote with your wallets - buy Gravity Falls merch (there were toy figures displayed at a recent toy fair, don't know when they're released), buy the game when it's available, make it clear Gravity Falls is a worthwhile investment.