I clean installed Windows 10 on my Dell XPS 17 L702x a while ago already and this post is merely here to indicate: yes, it works and it’s not even a big deal. This also got rid of Dell software junk preinstalled on my machine which is awesome.
Dell doesn’t support the Windows 10 upgrade though, which is why it scares people and your mileage may vary, but in my case the only thing that didn’t work anymore after the upgrade is my SD card reader. The drivers for that device haven’t been updated since the Windows 7 version and I didn’t find anything more recent. It took me a few months to find out it was broken, so that shows how much I need that thing.
So to summarize:
You can upgrade your OS or do a clean install with Windows 10, but your SD card reader will not work afterwards. If your life depends on that card slot on the left, it’s wise not to upgrade.
As always, be careful with drastic operations like this and backup your data first. For real this time. Plenty of stuff can go wrong and knowing that your data is safe makes it a lot less stressful if shit does happen to hit the fan.