Nintendo sources different screens for 3DS but adopts them “silently” without anyone being able to tell from the box. They could introduce new screens for the Switch without changing the consumer-facing product at all.
I can't see how there can be a release date for 2019 when Nintendo hasn't even finalised specs, let alone created a working prototype. At best it's an “aspiration” to release in 2019.
We here talking about difrent version of Switch where one of the things that will most likely be different among other things is screen, we dont talking only about screen difference.
They mentioned like summer of 2019. like possible release period for this revision, we dont talk about brand new platform or brand new console, just about different revision or type of existing device thats already out. So its not like they need years for something like that, they can finalise specs even in December or even in January/February and release it on revision on summer, there is reason why Nintendo announce this types of revisions and difrent version of existing hardware only month-two before launch.