The article points out that you can use their ISJSON function as a check constraint on your column, guarding it from malformed data:
> ISJSON( jsonText ) that checks is the NVARCHAR text input properly formatted according to the JSON specification. You can use this function the create check constraints on NVARCHAR columns that contain JSON text.
Not to nitpick. But you want this validation to be default. In this case which it can't be.
Question is what stopped MS to just wrap this NVARCHAR with json validation and json access and give it as json type. May be native json type will be added in future versions. I think just they wanted to ball to rolling.
> ISJSON( jsonText ) that checks is the NVARCHAR text input properly formatted according to the JSON specification. You can use this function the create check constraints on NVARCHAR columns that contain JSON text.