It's actually quite a bit different. Piece-parts of code could be lifted from one to the other, but nearly everything requires intensive review of the code to find and make the changes to the new method and function names, even with search/seek/find tools to look through the original files for the function or method-names that need updating.
The larger problem is that what worked in Civ5 for either a UI environment or a gameplay environment even when it has identical function-names and usages does not in civ6 work in both UI environment and gameplay environment. Attempting UI code in gameplay simply causes runtime errors. Attempting gameplay code in UI environments usually seems to lock the game as soon as the human opens the UI panel or makes the in-game action that would normally open the UI panel.
Nor does the civ5 lua file-contents "include" system work in civ6. Which means that for multiple files that were copying in the contents of a toolkit file in civ5, these entire toolkit file contents would have to manually be copied into each file that needs it for civ6, or else make use of Gedemon's somewhat complex system.
And this still will arrive at an lua interface that cannot directly communicate with gameplay state, which it needs to do in order to implement certain if not most effects of an InGame Editor like DonQuiche's IGE was.
In other words, even with the SDK out, we should not expect an in-game editor any soon if ever... got it. (Going back to Civ V.. first time I regretted that I bought a civ game... next time I will not pre-order and wait to see how is going..)