It's not beyond reasonable expectations that this could be used for International travel too. No country will want people coming in who could be infected and start spreading it in their country, so it could be that countries expect those crossing their border to either:
- Present a trusted certificate to illustrate they are Covid-19 safe, or
- Quarantine for 14 days upon arrival (South Korea are doing this already I believe) - which essentially kills tourism.
If reliable and not able to be abused, it would appear the best way to revive worldwide tourism, which will desperately need it.