I took some time to check how throttle bodies look after 1400 km's, including 500 km off road. Reaching air box on 1090 takes much more time than on 690, but it is pretty much straightforward. I do suggest following the manual, as there is a lot of plastic parts mounting on top of each other and mounting/dismounting order matters. I did some other mods, so I just disassembled entire front of the bike.
So far, so good, everything inside the air box is spotless.
Just for added safety, I am adding Unifilter air box dust seal (AU 1436 DS) and Power partsAir filter dust protection. Unifilter dust seal should prevent any dust coming through imperfections between upper and lower part of the air box.
It took some time and effort to place it correctly. That damn hose on the bottom of the air box wasn't making things easier. Eventually all went well. Next time will be easier, it always is. :)
I am keeping OEM Mahle paper filter, it fits very well. I just greased rubber lip and put it back in.
PP dust "socks" should prevent larger dust particles from filling in paper filter. I was hoping that there is faster way to reach PP dust "sock", so I can easily clean them from time to time, but you need to remove side fairings to reach them.
I will try to check inside of the air box for debris on regular basis, we'll see how this setup will hold.
UPDATE, January 8th 2020
After few air filter check-ups, I ditched Unifilter air box dust seal. It's not easy to align it well and I was afraid that, if not aligned perfectly, it can do more harm than good, so I am not using it anymore.
It seems that most protection is coming from Power parts Air filter dust protection, these filters are taking most of dirt and debris, and a lot of dust.
Searching for a way to upgrade air box filtration on 1090, I found interesting article on air intakes on overland vehicles, it is nice to see how this is sorted out on different vehicle types.