I dunno. I feel like the juniors would be kinda empty. Not in just active players, but it will be pretty void of excitement as it's just you doing things against bots and maybe the occasional other player. Would it be very fun and engaging for a new guy? You sign with a team and then are immediately separated from them? The league also won't have brands, history, history being made, or an identity. That doesn't really sound like something I would want to see my player in.
Not sure if this is a thing in hockey, it is in american football, but what about practice squads? GMs can easily swap them into sims and we don't have to do the intriguing, albeit probably meaningless process of a whole league for a small number of users. This would also keep users engaged with their team and their teammates.
This is just my thoughts. I imagine someone will say that the juniors league is just this but the idle players can see themselves get stats. But is it really that important?