Sync clearly makes sense for short games, such as Hearthstone, where most games last about ten minutes.
Despite polls surveys that indicate players prefer sync, it's obvious that will not be the case with Scythe. Sitting around a table is one thing. Online participation is quite another. Downtime at the table is enforceable but is unenforceable online. If I don't like my position or I'm bored, I can walk away - and that will likely have a negative impact for the other players.
I expect Scythe sync only will be a disaster. It doesn't make any sense. Btw, sync also pretty much obviates playing against friends who live a few time zones away.