I'd like to point out that Microsoft has been heavily investing in the last few years in extracting things out of stdlib and into nuget packages, heavily because they were not happy being tied to monolithic .net framework releases just to iterate on an API. So I'm not even sure how much they would even agree that having a fat stdlib is good.
Afaik pipelines isn't planned to be placed in stdlib, but will instead be kept in a nuget package that can be included if the application/library wants to utilize it.