I don't have a problem with other subclasses being played in the bot lane position. But I see quite a problem with how to implement it.
Riot is trying to implement as many subclasses in as many roles as possible. You can see it in their develops of the recent champs.
There was no marksman played in the jungle mainly. They designed Kindred with that goal.
Do you know about the early development of Bard? They wanted to create an assassin played in the support role, giving him mobility and stealth. But it didn't work out so they changed his kit to be the enchanter we know.
But they didn't give up, they finally designed an assassin/support hybrid with Rakan. His playstyle is pretty close to the classic assassin.
Riot tried to get other subclasses in the bot lane position before. Remember Mordekaiser? He was designed to be a melee champ played in that role. But it didn't work out well and he is in need of a VGU.
But that's the way I see it. It is hard to implement another subclass in that role, for us just as well as for Riot by creating a new champ for that purpose. But the case with Ziggs was a hint that it can work out if you get another champ filling the spot of the "wrecking ball". Maybe they will be able to implement new champs for that issue in the future.