Firstly, I am glad Moffat has come out & said this. It was what I and many other 'older Sherlockians' have been trying to say since Reichenbach. Whilst Moriarty was a master villain, it's over & done with now. The canon isn't like the mush they put out these days that keeps churning over something just because it was popular. You make a masterpiece, you move on. You don't keep adjusting it. I would say 'newer' fans would have been most familiar with Moriarty, but they need to look deeper, read more & watch more to see that while in some stories, there was no real standout 'bad guy', occasionally there was a monstrous one.
Yes, no doubt Moran will pop up at some stage, he'd be the next most recognisable one.

I'd suggest:
Charles Augustus Milverton

Sherlock despised that man wholeheartedly.
I re-watched that one the other day & have just started reading the original to compare. When I watched it, I saw so many opportunities for Moftiss. I could well imagine him being the villain that 'pops up' through the next series until the conclusion at the last episode (as they did with Moriarty) as his nastiness did span well over 12 years I believe. I don't expect 12 years to be portrayed in a series, but glimpses of his nastiness could certainly be thrown into any episode leading up to another finale.

If you want to watch the Jeremy Brett version ( called The Master Blackmailer) here it is here:




There are some comical parts in it, and this is the one where Sherlock stretches the bounds of decency by becoming engaged to a maid in the pursuit of justice with no intent of marrying her.
Wouldn't that be enough for some fans to go bonkers?? lmao

Oh this character will make you hate him so much.
The things against them using this one could be that they don't want to place Sherlock into another 'relationship' styled situation again being that viewers may expect to see that more often and I too would be wary of doing so. There's enough hysteria around in the fandom as it is! Also we've already had one storyline of blackmail, would it be too soon to do another & risk possible criticisms in comparisons?
But I think it's a good meaty story that should be done at some stage, twisted with a slice of Moftiss of course!

Possibly but he wasn't really any villain of note.
I do recall an interview with Andrew Scott where he basically said " it's been fun but time to move on now".                              Again I think people are reading too much into what is said hoping everything has a twist. Moffat's words are the best guide, he says quite clearly that you don't keep bringing a hit back because it loses appeal.

Damn you Moffat, although he's right of course, it would be bad writing to keep bringing him back. I'll miss Moriarty, although I'm sure he'll be kept alive by the fans in fan fic and roleplays!