Yet one more reason for regular oil changes with a good quality oil, it doesn't have to be a boutique oil like Amsoil, Redline, Driven etc. Just a good quality group 3 or 3+ synthetic like Valvoline, Penzoil, Mobil 1 etc.Not to mention the additional build-up on the backs of the intake valves from the oil consumption of way thin oil....
That is also another good case for applications of hydrogenated DLC coatings in ICE applications however (aka TriboTEX), because it enhances ring seal, thus keeping your oil cleaner for longer and reducing vaporization rates. It would also form on valve guides, so you'd get less oil seepage through the valve guides on to the intake valves. Follow up with a good OE quality paper air filter and even in a TDI engine you can limit intake valve fouling issues.
I do believe there are cleaning services available however, they use walnut shells to blast into the intake, then suck them back out to clean the valves / stems. Subaru was doing what for a while with their WRX's, not sure if other manufacturers are doing anything or if that is enough of an issue with modern designs / oil formulas.
But it also makes a good case for using an oil with a strong detergent package.