The Big N have announced that Switch Online will launch on September 18 (in the US) and September 19 (in Europe).
In addition to that, we will have a 7-day trial for everyone who signs up via the official eShop.
Consider this more of a brief introduction to what is coming hopefully at a later point today (via the Nintendo Direct event). That is when we will have much more info about the service itself. But, hey, nobody can stop us from celebrating right now!