I was one of those guys who had an upgraded trinket at level 9-10. I know this is probably only my own opinion, but I feel like not being able to upgrade the trinkets, combined with the inability to buy wards, feels absolutely terrible, especially when I'm playing somebody who can take advantage of the upgrade, such as Lee Sin or Katarina (hate all you want).
I liked being able to ward my river in mid lane. I liked being able to help out a support or jungler by being able to ward as I roamed. I liked to have my bases covered. That's impossible to do with the trinket as it is now. It scales incredibly slowly, being almost no better than a standard trinket at level 12 (about a 20 second difference on ward lifespan).
The cooldown is worse at level 17 than the non-upgraded trinket at level 1 on live, and only breaks even at level 18.
Speaking of level 18, the cooldown is double what the upgraded trinket is at level 9 on live.
I'd rather have the yellow trinket entirely removed from the game and bring back Vision Wards in the shop than what's currently in testing. It feels absolutely horrendous to use.