Current location tracking systems are vulnerable to misuse by authorities and third parties. You'd create a self-hosted or decentralized alternative with end-to-end encryption and strict access controls.
Privacy-focused individuals and organizations would pay for this, especially those in high-risk professions where location privacy is critical.
Start with a simple mobile app that stores location data locally with optional encrypted cloud backup. Add sharing controls later.
The biggest risk is balancing privacy with usability - too restrictive and no one will use it, too open and it's no better than existing solutions.