For HOMM 3 it was not the editor, but the MOD that kept me playing it... if anything that random map creator...
For any game having editor applies following: more maps does not mean better gameplay, but more disappointment from trying maps of "wannabe" map creators... For instance Disciples 2 got very easy-to-do map and even campaign editor, but if you look in net for maps, most of them are crap, I was sorry for the time I spend searching and downloading them... and yep - I played the game longer as I have created my own maps according my game taste, but the best game experience was still from the professionally crafted maps/scenarios of the original...
I have played old KB (dos version) very often and very long time, and returning to this old game from time to time again and again... and I did not miss scenario editor...
When I look back in time how I enjoyed the maps in KB tL made obviously by real professionals who payed attention to smallest details, I would not ask for scenario editor, as the only I could change would be the random armies and also I would lose the feeling of revealing the "unknown" as there is no revealing when you create a map...
Would I welcome scenario editor in KB tL? - yes
Would I miss it if it would not occur? - no
What would I like to see in Expansion, if not scenario editor? Duel mode - where you can design your own hero + skills + army + spells, and try it in Hot-Seat mode with yourself or your friend, who would design his hero... this would be interesting to find out if dryads are really so strong for instance
