Law enforcement should require a subpoena if they want to have location data for anyone. It really isnt a third party loophole issue.

Law enforcement should only be accessing location data if they have probable cause to believe a crime is happening. This invalidates the third party doctrine loophole and becomes an unreasonable search (and seizure of your privacy) under the 4th amendment.

Location data specifically should be treated as the most private data about a person. It should have the highest scrutiny for any access. It is more important than your financial records and medical records.