I've been on this site for a long time. My Low 6 digit number should be a testament of how long I've been on this site. Hell I don't Even use Deathlizard any more as my handle on any site but this one. but I can tell you what my Display Options are set to.
1) I Use the Classic Interface because I like the classic Interface. It's simple, Loads fast, and gets me my News For Nerds and Stuff that Matters.
2) I use the Classic Discussion system, and not the one that was reworked the last time the site had a modernization.
What makes this site special is the simple fact that it is so customizable. I don't have to update my look of the site but others that want to can get the new whiz bang tech site that the kiddiez crave. I can keep it the way I want and the Kids get the new wave look because they are either not logged in or they signed up with a new account with the look turned on by default.
I know it would be a pain to maintain both looks, especially since it looks like they want to do away with the generic icons as news points and replace it with stock photos, but I can't imagine it being so hard to maintain when it's pretty much been the same for over 15 years now and pulls data from the same database, and I think it would be worth maintaining rather than lose your user base to other options or even to a forked, Slashcode running, classic slashdot site.