to those that have skated the t1 inverted. how big of an issue is the the kingpin loosening? Is it worse if you run them tight and cranked or on the loose sider?
For all the sets I have sold in the shop and skated myself, I have not had one set with any issues or one kingpin loosen itself off, apart from one of the first sets I got with the hollow kingpins that was passed around for people to try, so it had a lot of doing up and undoing swapping in and out bushings a whole lot more than the average person would do on their own setup.
Even on this set which I got back and I am riding now, I marked the head and they didn't move too much until the hollow kingpins broke (which is why they changed to solid kingpins) and then swapped in some other solid kingpins and they have not moved at all now - been skating them for a good number of sessions and everything is ok.
I really think that the main issue with the kingpin undoing itself comes from the nyloc degrading over time and only then if people are constantly changing things, tightening or loosening, or swapping out bushings a whole lot. I even bought a little bottle of Loctite to use if needed but it is still unopened, as the trucks have been fine without it.
My own trucks have stock 90 duro bushings and loose enough to turn to just wheelbite with all weight on one side, but tightened enough to hold everything together and give a bit more kingpin clearance. Other people ride various assorted tightness and haven't had the kingpin do anything funny for them. There is a little more movement in inverted kingpins than regular kingpins that I can see when I look down on the board and move the hanger from side to side with my hands, but I am fine with that and they skate well for me.
Also just to note, if a Thunder inverted kingpin breaks, the trucks are covered under warranty, just to put that out there too, which some people might not know.