ive heard of 19-20 footers in hawaii and jamaica. I suppose with genetic manipulation and the right facility you could get more. i would think though the better option would be to find a way to produce larger trichs.
could you imagine if they were the size of a grape?

they do die at the end of fall i have seen wild stands they do their normal thing dump a ton of seeds and grow back. thats why they dont get the size of sequoia trees. they also have a limit to vegging i believe.