The unfortunate side effect if this became standard is that there may be far less motivation for wealthier nations to help poorer nations vaccinate everybody.
Anyway, the travel restrictions I mentioned would hardly be bulletproof. Vaccinations don't confer 100% immunity, and tests aren't 100% accurate. So countries could still reduce their risk by supporting worldwide vaccination.
Also, this might be a moot question if we can't produce enough vaccines to do it all at once.