I know how things have basically gone now, but when I look at people talking about Gotham when it was new, they tend to say that the writers were planning to introduce several characters who could be The Joker, but it was going to be unclear. The way they talk about it makes it look like (or outright says) that this meant that the plan was for there to be literally many potential Jokers, possibly ranging from obvious candidates (like Jerome), to possible candidates who fit in with versions of The Joker, who aren't quite there yet (like the comedian in the first episode), to possibly even characters who are nothing like any version of The Joker, but could still have their "one bad day" at any moment.
They may have sort of done this - there is a page on Legends of Gotham entitled "Look At This Joker!" which detailed possible suspects for the future Joker, many of which I never even thought of, but was this ever the actual plan of the writers, to have several potential Jokers in the show, presumably some more obvious than others?
Ultimately it ended up being all about Jerome and later Jerimiah, which seems a shame to me, as it sounded cool having several candidates throughout the show, rather than mostly one super-obvious (but nicely acted) red herring, and his brother, especially with TV Tropes tropers theorizing that they were going to include characters who had personality traits of the different incarnations of The Joker from years gone by.
EDIT: Yes, I am also aware that the writers apparently can't use The Joker and call him The Joker.