Re: v5?
They are talking about .NET 5 (aka .NET Core).
Other than that you probably should be aware of Microsoft numbering theory:
Version 1: Incomplete and broken
Version 2: Fixed version 1, but still lacking features
Version 3: What users actually wanted
Version 4: Reimplemented (and with incompatible bits to V3), fancy bits added, but broken.
Version 5: Version 4 fixed.
Versions 6 and onwards: Rinse and repeat steps 4 and 5.