wich: For anyone who runs into this issue nowadays and came here through a google search:
Since gog is using a ScummVM based installation of GK2 these days going back to interlaced video is actually trivially simple. You only need to edit the gk2.ini file in the installation directory and change the enable_black_lined_video to true.
TwoSouls: Just jumping in here to say that changing the .ini file does not work. Would love to get interlacing back if possible...looks so much better that way.
It seems that the ini edit (which is a ScummVM configuration file) not working for this issue, is known and there's little the ScummVM team can do about it.
Here's the relevant ticket with comments from a developer on the ScummVM bug tracker:
https://bugs.scummvm.org/ticket/9751 As far as I know, there's been no PR submitted since that ticket was closed, so the issue, which indeed is not a trivial one to solve, persists.