Nintendo already has Nintendo direct, so I don't really think they'll have their own show. Microsoft on the other hand might follow this. Maybe if these events gain alot of momentum and fans start talking about it more, then maybe E3 will start getting weaker by the years. However this needs to develop much further and become the norm for it to replace E3. This gen E3 was not the place where Sony and Microsoft revealed their consoles, so maybe E3 is actually starting to lose its importance by a bit.