Snyder said he found Jesse Eisenberg 'scary, smart' when interviewed for the cameo of Jimmy Olsen. At that point Bryan Cranston was Lex.

They re-wrote the part as Lex Junior for Eisenberg.

They don't explicit say in the movie that Lex Senior is dead, so there's a very feint hope that Cranston can still be in the next movie.

...but bear in mind that they removed the S in Batman 'vs' Superman because S stands for hope! lol

regards
prixat