I'm trying to guess at the same thinking, "longer veg time?"...may I share my thoughts about what I've been reading so far?
*SoG - Sea of Green
Concept, many plants in a limited area, many main colas. Short veg, most growing done during flower?
*Cannabush - includes LST (Low Stress Training), Topping, FIM'ing, SuperCropping?
In regards as to eight weeks being too long, I'm thinking if a single plant is used to create a bush and grow several colas from a single main stem, then you will need an increased amount of branches. If you have more branches, you need time to grow these out enough so they will be able to support all the grow sites. "Grow these out" means considering your containers in respect to avoiding root bound ladies.
(Soil) Based on the theory that the roots use soil and it's nutrients to literally form the cell structure of the plant, it would be unfortunate should the plant run out of usable raw materials. Transplanting to bigger containers would allow more raw materials for the plant to utilize. If using soil, and going after a bush, I can see eight weeks of the raw material being used by the plant in order to grow and strengthen those multiple bud sites into a nice little (large?) bush.
More veg time allows time for branching, recovery from topping and FIM'ing, LST and supercropping I think? Keeping in mind that as time passes, she's still getting bigger and bigger, and you haven't hit that flowering Growth Spurt yet.
Would a long veg time be opposite for SoG? I'm thinking since SoG concentrates on the main cola, side branching and additional colas would not be the goal. Additional time would not be needed as the main cola would be able to fully utilize the available nutrients in their given container before becoming root bound. In addition, the longer the veg, the more likely the lady will grow bud-site covering fan leaves?
By no means a complete thought, and I totally left out the hydroponics aspect, but I was considering a "bush" down the road somewhere and have been toying with theories.
Actually, what are you hoping to achieve by additional veg time?