Hmm good point, Leveling to TL5 as a froob isn't THAT bad. 150-200 is the hardest part anyway. Would be interesting if SL was really only for higher levels, but then again I kinda hate that concept with the LoX booster. ALthough SL would still grant perks I suppose. Imagine a level 150 nasence? inferno could scale to be way harder, level 250 normals? Pande would be incredibly hard again.
Not a viable suggestion, but great thought for what couldve been (which you said anyway ^^)