The problem is when that remaining 10% takes way longer than expected.
Especially since this is only part of their Business product for now.
Looking at you Google Drive.
Not saying they're doing that here, I'm sure it'll take time to implement.
Linux is also a much larger target than Mac OS or Windows ... different filesystems, desktop environments etc. etc.
You're looking at the wrong end of it. Dropbox doesn't have to deal with any filesystem, Dropbox instead needs to build a filesystem.
It doesn't have to deal with any filesystem because Linux abstracts it. The same abstraction allows it to build its own filesystem really, really easily. How easy? I wrote, mounted, and used a filesystem in less than fifteen minutes. In node.js. It's that easy.
> desktop environments
Dropbox doesn't need to support various desktop environments, just a stable API for the desktop environments (actually, just file managers) to use. Isn't this how Nautilus, Thunar, Dolphin et al. already support Dropbox's existing features?
After all you can bypass the problem by running a Windows VM in VirtualBox with guest additions and a shared filesystem. Is another way to map the Windows Dropbox's network filesystem to the Linux one, whatever it is.
Still, very cumbersome and probably slow. I remember not stellar performances with sharing files between host and guest OSes in that way.
Hopefully Dropbox will release the API and somebody will write a user mode filesystem to interface this new service.