Reducing the number of foreign players will not likely take a toll on ISL viewership...
You often come across a person who has changed his job for a better remuneration, a non-vegetarian converting to a vegan or one who has filed a divorce after being years in a marriage. If you are lucky enough, you might even find an East Bengal fan who distastes Hilsa or a Mohun Bagani who doesn't like lobsters.
But seldom you would find a football fan who has changed allegiance or has stopped watching the game even when his favourite team is underperforming.