The problem isn't the lockouts. They could easily limit everyone to one difficulty level per toon, or make it Mythic/lower three shared.
The problem is gear inflation, which really has nothing to do with LFR and everything to do with 4 difficulty levels. Leave LFR queueable, eliminate Normal, let guilds do heroic/mythic. Institute a lockout so that heroic/mythic can't do LFR. If people want to smash their faces into 5 split Heroic runs before they hit mythic more power to them.