Pretty damned sure that the chances of getting any 'pure' strain is no longer possible. I believe that all strains on the streets today are going to have been bread with another type at one point in it's genetic make-up.
There are still 'pure' landrace genetics around, it's just that most growers don't bother because they want high yield and quick turnaround due to greed. Most of the hybrids today are designed for easier indoor growing, fast maturity, and high yield. Bubblegum is a hybrid but is Indica dominant.
Off Topic, I feel the need to read your "book" again. OT: I'd like to grow Sativas, but with the setup I have now, at home, not likely. From what Sativas sound like, I feel like I'd love them, but sadly, they don't come around here, nor do I have the time to grow it.
That's my only reason why I can't. Height doesn't really matter to me, because there are ways around that, like you said, LST. Example, I would love, LOVE! to smoke legit Buddha. It is one of the strains that I need to try.
Like I said it just takes patience. Most pure Sativas mature in around 100 days or so after going into flower.