What key would be a good candidate as a default though? Imagine the memes for exiting vim if you needed a modifier to get into normal mode. Caps lock is truly a useless key and should be escape anyway.
<ctrl-[> always works out of the box which is less of a stretch than esc.
I do jk as I always find a roll easier on the fingers than a double-tap jj or kk. You could also use space provided you aren't using one of those distros that bases its identity on the spacebar.
As someone who cut their teeth on a sun "programmer" layout, I really need control to be in that position. I might try mapping the vestigial control key to escape though. Or maybe the hack that dtj1123 describes (tap is escape, hold is control), if I can pull that off on macos.