Jokes like this that affect regular use ofIf a joke on a site used by professionals is taken so far that it slow down or obstructs ordinary usage of the site, going that far should be opt-in. Regarding this:
I do understand that making it opt-in would ruin the feel
ItChanging the entire site to a barely-usable 90s-style design could have been opt-in, without spoiling the joke.
Have an opt-in notice like the opt-out notice pointing at the clock icon, but have the content of that opt-in message in full-on 1990s-style, with comic sans, a red scrolling marquee saying CLICK HERE TO TRY OUR GREAT NEW DESIGN!!!!!!!!, animated flame gifs around a blue underlined "CLICK HERE" at the bottom... but only inside the box pointing at the button, until the user clicks on the button.
If it was done like that:
- People who weren't in a hurry would get the joke, laugh, click into 90s mode and have fun
- People who were in a hurry could just do the task they came to the site to do with no hassle
- The inevitable unexpected bugs (like load time slow down, cookie failure, site-specific CSS problems) would matter much, much less, because they'd only affect people who had opted in to a joke.