None of the things you count as "good" are considered good by me for a gear threadmill.

• "Implementing challanges to constantly overcome" is equal to "invalidate everything you achived so far constantly". Masteries show a better approach to this.

• "Stats are numbers, and easy to increase. meaning that you have an increased chance to have new stuff to do." is the same as point 1. Even with your later example you jump from fine to exotic gear, neglecting rare in between, because once it's all about the better stat, nobody bothers with the steps to them unless you make it needed... thus a grind that gets constantly invalidated. I don't see how higher stats give you opportunity to do new stuff either. Masteries will do that without invalidation though.

• "with the introduction to Gearscore in some of these games, they can implement gates that prevents poorly geared characters from entering hard dungeons, even groups, making you able to alter the required gear level" is not a good thing either, it's dividing the playerbase into certain levels to the benefit of nobody. An undergeared character might easier find other undergeared characters to team up with, only making it harder for all of them. Now however, you may have 1 undergeared with 4 fully exotic players, and they will do fine. Separating them serves nothing at all. The only motivation behind this is to not only feel better than them, but to actually are by stats. This is not an inclusive or friendly system.

What you propose is not a gw2 solution because of the points above as well. And lastly, we heard it in the manifesto and again in january: Arena Net does not want the threadmill. It will not happen. And I for one am very grateful it won't. I have played enough MMOs and found myself despising those systems.