I'm just preparing the MSI packages for the final Inkscape 0.92 (yay!) and noticed we still do not properly support updating old installations:
* The fix for bug #1418595 (see [1]) allows to update Inkscape (the Product Id has to be updated for this). The problem is that we do not really uninstall the old version in the process (at the very least we end up with duplicated uninstallation entries and program shortcuts - in the worst case this might also be true for installed files which would be very bad and needs further investigation)
* As a second issue that has to be considered when fixing the above we have bug #1418274. In short we have to decide how to treat parallel installations of different versions (i.e. 0.91 / 0.92) but also different bitness (32-bit / 64 bit).
[1] http://bazaar.launchpad.net/~inkscape.dev/inkscape/0.92.x/revision/14007
Chiming in to hopefully get bug #1418274 resolved, maybe the importance can be increased as these remnants and left behind items make deployment situations tricky.