I haven't been following German politics: Is it actually feasible nowadays that the Greens would ever be in a coalition with the Christian Democrats but NOT the Social Democrats?!?
Jamaica is certainly difficult to put into practice (mainly due to the aforementioned CSU/Green friction), but not entirely impossible.
However, I'd estimate that it would be require both Red-Red-Green and Traffic light either not getting a majority (while Jamaica does) or coalition talks between those parties having broken down first (while talks for Jamaica don't).
At the end of the day, forming a coalition with
both CSU and FDP at the same time would be a pretty bitter pill to swallow for the Greens. A coalition between CDU and Greens alone - like it is done on the state-level right now - is much more feasible. Chances for Jamaica will probably higher if the Greens have a stronger election result than CSU and FDP and hence are in a stronger position within the government.
So, there are big question marks, but it's not completely impossible under the right circumstances.