I'll believe it when I witness:
1) porcine flight
2) their appearance on the grid
In that order.
"Evaluations" are a dime a dozen, which is far from the millions needed to commit.
Miller places the odds at 20%. Pruettt thinks IndyCar is being used as a pawn against Liberty, or more succinctly, "garbage."
FCA was also rumored (via Alfa), but that died with Marchionne.
Personally, I'd rather Ferrari get serious about sports car and do an LMH program, or LMDh, if they go back on their stated desired to build their own chassis.
You're right, if Ferrari expands their motorsport program it should and probably will be in prototype sports cars. They haven't been in that category since the 333SP IIRC. Indycar isn't a good fit for either.