It’s not uncommon for LEGO Technic components to be included in LEGO builds - especially where motion or interaction is needed.
Has the same ever happened with a Duplo component being included in a ‘classic’ LEGO set? Perhaps using their extra size to help build up an area.
(In case clarification is needed, we can define Duplo components as being anything listed under Duplo in the LEGO pick-a-brick service. And any set not branded as Duplo or Technic can be considered a ‘classic’ LEGO set).
One instance I can think of is the 52 mm ball, usually used in the DUPLO Ball and Tube system, being present in a couple of "classic" sets. Most notably the Indiana Jones Temple Escape, 7623
https://www.bricklink.com/catalogItemIn.asp?P=41250&in=S
It's also present in quite a few Mindstorms and Technic sets, where it is usually used as an object to be grabbed by a gripping mechanism.
There was almost (probably) a Technic BIONICLE set with a Duplo tread piece.
That set would have been the Sand Tarakava (low-res, high-res, other), a smaller set that was meant to compliment the 8549 Tarakava set.
This prototype set was given to Saffire to develop the cancelled 2001 PC video game, and later changed hands.
Ultimately this set was not produced, so it's possible it would have undergone additional revisions if it had been. Changing the tread seems like it would have been a rather drastic change though, especially compared to the minor changes seen in other prototype models Saffire worked with.
