I'd also love this as I specifically bought BTSync/Resilio because of it's git like ignore syntax that allowed me to sync my development folder without the million node_modules and build artifacts.
I just set up a new machine today and noticed it syncing loads of crud before I caught it and updated the .sync/IgnoreList file. Considering git brings it's ignore with it, I also expect some method for git-like ignore lists to be synced as well.
Just give us an option, or another file like .sync/SyncedIgnoreList
