I can't see how such a merger will change much. IHeart will still be IHeart, and SXM will be the way it is. SXM is gradually losing listeners / memberships, and IHeart has one foot in a medium that is slowly losing listeners (terrestrial radio) and the other foot in a streaming platform that only has around 8% of the younger demographics, who mostly are listening to Spotify.
I suppose a couple channels on SXM might change, and maybe the IHeart online streaming platform would adopt some of the SXM online channels. I can't see how it will change much else.