Tile Yields were nerfed to accommodate 1UPT since you didn't want scads of units creating carpets of doom and enormous traffic jams. Not that it didn't happen on a regular basis anyway.
This had a disastrous chain reaction on the rest of the game. Production times had to be lowered and improvement times had to take a lot more time.

Things moved a long slower and it killed the pace of the game.
In Civ VI, you have an easing of 1UPT to an extent with limited stacking as well as support units being incorporated into other units. Workers will be less numerous since they will have limited charges. So with that, perhaps there can be an increase in tile yields since units will be less numerous overall. Less units = hopefully less traffic jams.
Builders will also build improvements instantly so that is a variable they won't have to take into account with tile yields, as well.
If tile yields are higher, districts will make for some interesting decisions. Do you want to use that high yield tile for it's yield or do you want to build a campus there?
IIRC, Citrus from one of the videos seemed to yield 4 food and I believe that was unimproved. Of course, these things are subject to change but perhaps that might give a very rough idea of the way they are headed.