He will have my vote most likely, if he wins the nomination. I've been a fan of Weld for a long time, and he was a big draw to me to vote for the ticket last time. He's an intellectual, charismatic, moderate libertarian choice who could win a lot of appeal in mainstream circles and bring a bigger tent to the Libertarian Party, and be a plausible "NeverTrump" alternative. He'd get high profile endorsements, media attention (and unlike Johnson, he wouldn't botch it), and I think he would be a legit contender and would get into the debates.
I hope he runs.