before 2020 for sure. I can totally see her giving us a big tour in her 60's. She won't call it a "farewell" though because it will sound like she's retiring. She does need to take a break from touring because she's been touring non-stop for 15 years and a lot of the markets are over-saturated.
We'll have one more big scale tour. Her Live Nation contract requires her to fulfill another world tour by the end of 2018.
But you're right, I think more intimate shows is what we'll be seeing more of in the 2020s. I love her to death but realistically, she can't fill stadiums or arenas forever at the rate that she tours.
This will be my first Madonna show, and I'm hyped to say the least.