OneDrive needs to behave more like a cache
There're actually six sync engines if you count the Office 365 synchroniser. It's a shame that there is such confusion at MS that even their senior managers can't keep track of how many different versions of essentially the same thing different teams are maintaining.
The solution to this ought to be to have just one version, embedded in the Windows OS and as an app elsewhere) and scrap all the others.
Secondly, it needs to operate like a traditional cache and not as something that the user always has to be aware of.
When I installed OneDrive it immediately slowed down my system because instead of getting files from my very fast SSD it went first to the online version. To avoid this I still have to manually make sure I open the local version.
The placeholders are brilliant and work well on my Nokia 2520 tablet and 1020 phone. However, again there is too much user intervention required to manage this. Many apps in full W8.1 crash or just do nothing if you try to open a placeholder and you have to manually download it first. Applying a cache philosophy would make the whole thing more transparent to both the user and the app, use fast local storage when available and slower cloud storage when not.
Office 365's live collaboration tools need to be disabled by default for the 99.99% of people who will never use them. The problem with making sure that the cache has the required data when the machine state changes (e.g. when on an airplane) is also easily solved.
Microsoft also need to address the issue that such poorly architectured software made it into release versions of Windows 8.1/Office365.