Biggest problem would be Tulsi Gabbard's record. She has ties with Anti-LGBT and Anti-Muslims groups, and is opposed to basically all immigration and gun control. She is way more conservative than the average Democrat.
Plus I don't know if a ticket without a Christian can be viable. Kander is Jewish and Gabbard is Hindu.
-She is ever so slightly to the Left of Tim Kaine according to DW-NOMINATE. And there's no proof moving right on social issues and immigration is a losing strategy for Democrats. Remember, HRC got fewer votes than Barack Obama in Dearborn, Michigan, which should really be an embarrassment for Her, since Mitt Romney wasn't threatening a Muslim ban.
Mitt Romney was not a Christian, and he still won the Evangelical vote. Democrats care even less about Christianity than Evangelicals.