One of the biggest challenges we faced last year with Ember was sync. Once you start using Ember, it’s incredibly easy to build up a substantial library - and customers upgrading from LittleSnapper have sometimes many thousands more images imported! Multi-gigabyte libraries are not uncommon, and combined with (in particular) iCloud customers have found sync to be problematic. It especially doesn’t help that iCloud is a very hard-to-inspect black box, and there’s no progress shown to you as to the uploaded (or not) state of your library. It’s tough to say it, as iCloud’s robustness has continued to improve each year, but right now iCloud isn‘t a good fit for apps like Ember, and our future product direction will reflect that.
Last year they were optimistic that iCloud Core Data would improve. Now—three plus years after iCloud Core Data shipped—it sounds like they are giving up on it.