It is a valid solution, yes. Just as Seasons cap your hours at around 2200, shorter leagues 24/100/500 hours while the Season lasts with respected LBs could do the work. The problem is really the implementation of something like this and that it kind of splits the playerbase, while hard caps on the Seasonal progress don't. We all know D3 team is not so big as when the game was released, so will they decide to invest resources to fresh up the Seasonal mode with leagues or main stat/paragon cap, we have to see. I personally think both options will improve a lot the Seasonal play.
NS is pretty much useless competition wise. It has to be the place where people have no time/power limits in order to perfect their characters, but with so many botters dodging previous ban waves it turns mainly into "grinding paragon" competition, with the legit players hoping that all botters will receive the "hammer" at least once before the 10k finish line and there will be no people who devote 3 years from their lives on one account sharing it 24/7.