It was/is rumored that Canadian trucks already have the 4 leaf springs on their trucks now.
Per Toyota, you should be able to haul the same amount as the people that are getting the TSB done. They have not and legally can not specify a new amount for those that do not have the TSB. If they come out and say that without the TSB you can only haul 300 lbs, then they could be sued (happened with my Dakota R/T).
Long story short, you can haul the limits set by Toyota whether you have the TSB done or not.
07 and up Canadian tacoma's came with the tsb leafs, they were installed as soon as the trucks got to the lot. i hauled about 700lbs of rock in my bed sunday and was about 2 inches away from my bumpstops, and didn't hit when driving home. fyi i have a double cab long box.