The current one is fixed for 5 years, so no changes in the 10-team format till 2027. If we go by their previous expansion pattern then they would like to add a few teams (at best 2) in every new cycle(given it's 4-5 years for every deal). That's why I came up with the number of min 20-25 years.
I heard that the current media rights deal for IPL includes clauses for an increase in payment in case the number of matches per season are increased (it doesn't mention about the number of teams though). Your argument is valid though. Adding 3-4 teams at once can disrupt the equilibrium, as some of the franchises are finding it hard to get enough number of quality Indian players (Sunrisers Hyderabad and Punjab Kings are examples). Increasing the number of teams would further dilute the player pool, which will probably force the BCCI to remove the limit on overseas players.
I guess atm we have more than enough talent, it's just SRH, and Punjab are both struggling due to their management. In the context of "limit on overseas players". I believe this might not happen because ICC is discussing the possibility of a cap on foreign player's inclusion in the playing XI (Max 4).