I was running in to the same issue, but have just managed a full uninstall by means of trusty old CMD:
D:\vs_ultimate.exe /uninstall /force
Where D: is the location of your installation media (mounted iso, etc).
You could also pass /passive (no user input required - just progress displayed) or /quiet to the above command line.
EDIT: Adding link below to MSDN article mentioning that this forcibly removes ALL installed components.
Also, to ensure link rot doesn't invalidate this, adding brief text below from original article.
Starting with Visual Studio 2013, you can forcibly remove almost all components. A few core components – like the .NET Framework and VC runtimes – are left behind because of their ubiquity, though you can remove those separately from Programs and Features if you really want.
Warning: This will remove all components regardless of whether other products require them. This may cause other products to function incorrectly or not function at all.