For the base game I doubt it would make any difference. The cutscenes are handdrawn in 4:3. Expanding the screenspace would give you also black borders. You need someone to expand the drawings beyond the 4:3 aspect ratio by hand. Like the additional artwork for the menu and statistics screens in gzdoom.
In this case it works. Because this is the polygonal ingame graphic. There is still more geometry outside of the screen.
But the cutscenes are handcrafted pixelart with a defined size. There is no more to show outside of the screen.
Take this example from Hexen. Its the 3D graphics and bitmap combined but it will do the job. You can see the arm is cut off on the right side because there are no more pixels outside the 4:3 boundry. The same for the cutscenes in DF. Stretch it, letterbox it or crop the frame and loose parts of the picture on the top and bottom in widescreen (like old movies). Without additional touchup of the cutscenes, there is no other way.
Expanding the screenspace would give you also black borders
Hehe , that only knows Lucius , when he try it
Some Cut Scenes moves horizontal , that is also enough Room for Expand.
Here an Example : No one Lives Forever
First is the 4:3 Original from 2001 !
God, I love NOLF and NOLF2! (probably more than Dark Forces to be honest) If anyone reverse engineered that to make an updated engine it would be amazing. Particularly as it appears to be in licensing hell and none of the parties seem to want to figure it out.