I don't think this is going to directly affect NSO. There is no reason Nintendo can't use servers now, the reason they don't is they know P2P is a lot cheaper. Nintendo has partners already that could make a much better online system, they just don't care to.
I highly doubt we will hear anything official about this until at least next year, if then, and I doubt we will see results from this until very late into the Switch's life at the soonest, like 2021 or 2022. Its going to take a lot of R&D, and if Sony is just starting, Nintendo will be a bit further behind. Plus Nintendo absolutely doesn't need streaming ATM. Microsoft needs to start sooner in order to start testing and doing R&D, plus Xbox One is third worldwide so they kind of need the extra users, Nintendo is fine and their current strategy kind of revolves around the ability to play offline. I don't see Nintendo launching any Azure service until streaming becomes a clear player in the industry, and again, at the soonest that will be 2022, even if Stadia does well I doubt it will hurt Switch too much in the short term.