Segregating domestic and international traffic has been tried in a number of cases and has usually failed miserably. Montreal was a disaster, Tokyo didn’t work too well, likewise Paris. Moscow.
The reason is that the global networks are built on the hub and spoke model. Longhaul airlines need shorthaul feed and that includes domestic. Connecting passengers don’t want to trek from one airport to another, they will fly to a foreign hub and make their connection there.
A couple of exceptions are Washington National and New York La Guardia, where there are statutory limitations on the nonstop distance that can be flown from them, which rules out international flights.
Many airports of course have separate terminals for domestic and international flights. Domestic doesn’t need all the infrastructure elements such as passport control and duty-free.