I don't think there is anything that the upgrade kit addresses that is something that would leave you stranded. Every comman issue has symptoms that are noticeable early on. In my case, my issue wasn't related to anything addressed in the upgrade kit. It was discovered while doing the upgrade kit that the TDU was bad. My output shaft bearing was installed backward and it was still OK. I was told by my local dealer that the cut-off build date for the upgrade is 11/07. Also they are finding that what they originally thought was the cam gear rattle, was actually the oil pump drive rattling on warm up and they claim it does no harm.
I think they do have a policy, if your bike has any of the symptoms and a Triumph mechanic can verify it, then you get the upgrade regardless of the mileage or warranty period. Reading some of the things that dealers have said and done I would venture to guess that maybe 25% of the dealers in the US are competent enough to do the upgrade kit. Let alone to make it worth their time for the amount of labor Triumph pays for it.
Triumph could have done what most manufacturers would have done, silently upgrade the next model year and not acknowledge any prior problems. Who knows, if there are enough that need the upgrade kit, maybe they will make it a TSB for all of them.