After Greece where do they go? From memory they have now done the middle east, Venice, Rome, United States, Caribbean, North America again, Paris, London, Egypt and Greece. Only talking main entries. I may be forgetting something. So there's no 2019 AC which is good. But the 2020 release will probably be a cross gen game. So where will they go next? 

It should just stop and take a rest for a few years.

Your OP has a typo, it should should say now done, not "no done" 

Well I think they should go to China next. It would he awesome there. 

This is my biggest gripe with the series. I like to get the platinums in the AC games so naturally having so many to play gets tedious. I'm playing syndicate atm but when I'm finished that I'll still have origins and Greece to play. Good news is I'll have 2 years before another comes out.

Since launch they have pretty much released a new one every year and 1 year we even got 2, rogue and unity. That's just 2 much so hopefully moving forward they stick to every 2 years. 

I've been wanting them to do one in asia samuraininja times for a long time now. Just seems so obvious at this point I don't understand why they haven't done it.

The obvious place now would be China or Japan (yes I know they did a side scroller in this era but a proper game would be nice).
There’s other eras in locations they’ve already been. The Dark ages in The UK which spanned around 6-700 years, play as a Celt or something only problem is lack of high structures, or wait till the Viking age and play as a invading Viking.
There’s got to be somewhere in Africa we could maybe go to,

They could always go into the future and make some sort of futuristic assassins creed, still with the current weapons and the city could be all massive with incredibly high buildings.

As many have stated China or Japan would be the obvious choices.

If they're going to do anything to do with ireland then the viking invasion and settlement of certain Irish ports would be the best. They could have elements similar to black flag. Sailing between locations in Ireland, Scotland, Wales, West England and Iceland. 

If China and Japan is the obvious choice where do they go after? A location in Africa where the British, French or Dutch invaded? 

I would love to see one in my country, and there's also a lot of history to cut from. I'd like prehispanic Mexico you know with the Aztecs or Mayans, or during the Mexican Independence or revolution. It's just a thought,