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I think the next revision of Switch will be smaller with better battery life but probably no performance increase (not even docked mode when portable) and at that point it will have a form factor and price that fully allows it to replace the 3DS. However saying that its quite possible the revised Switch will sell concurrently with the original Switch for sometime. I think the revised Switch won't have removable joycons and docked use will require a purchase of controllers to use with it so the drop in price i.e. £199/$229 approx will be more acceptable to those who bought the original Switch.
I don't think it was ever realistic to expect Nintendo to drop the 3DS range day one and the new 2DS was not a surprise based on their past actions.
Their gameplan seems well judged so far. My own personal issue with Switch is poor value for me at the moment just not enough unique new game experiences to justify its purchase. I have no issues with the performance level except when people over-state it which I don't think helps anyone and leads to unrealistic expectations.
