There's a workaround if you want it enough.

I noticed that reddit was setting a use_redesign (I might have the name slightly wrong) cookie when I explicitly visited the old.reddit domain, and this caused old reddit to persist. Since I do occasionally want to use the new site for image posts and the like, I set up a bookmarklet to set/unset that cookie on command.

I've since found that setting this cookie bypasses the old.reddit login page, allowing me to view the old site while not logged in. No idea how long that will last though.