I can't see promotion/relegation working because some teams would have to willingly agree to, potentially, lose money (unless they equally shared money across division).It became boring the moment they had 10 teams playing each other.
The alternative,given that they want to add 2 more teams, should be to divide the teams into groups of 6 each. The Top can go into a Super Six sorta structure thereafter.
If the IPL keeps expanding,the only choice to avoid spectator burn out is by introducing the promotion/ relegation concept.
Can't see any other way tbh
I don't know how likely further expansion is, but that might lead to two groups which might make it more interesting.
Ultimately, even the IPL falls victim to the the long league stage, short knockout stage like all the other franchise leagues. Only the Blast and SMAT seem to navigate that, by virtue of having enough teams to keep it somewhat interesting thanks to an extended knockout.
From what I've read viewing figures have increased which would suggest change is unlikely and, if anything, more of the same is what would be desired by broadcasters and the BCCI.