Early June.
It's hard to say for sure but I imagine r5 6* will be a thing in 2021. Hard to say for sure though . I imagine it depends on how fast the story content comes out as (usually) they release the materials you need for new rank ups as rewards for story content. I would imagine that around this time next year it won't be unrealistic for people to have 5/65 6* (provided 65 is max level I don't even know tbh).
Early June. That's cool, unfortunately, I only have 5 6* champs which are all at r1. I'll probably never be getting a r5 6* much less a r3.
Rank 5 6-Stars are actually ready now. My first one will be Guardian because of how high his defenses are.