I've been using the CAPS LOCK as both Control (on hold) and Escape (tap) for years now, and it's just wonderful. I even kept a similar setup when I built my Dactyl Manuform (one of the large thumb keys is both Control and Escape).
If I were ever to design a keyboard with a thumb cluster, I would separate out ctrl and esc to separate keys. When typing quickly, I occasionally get an esc when I wanted ctrl. I've tried fiddling with the delays, but I've never gotten it to work quite right 100% of the time. I suspect my timing (how long I hold the caps lock button) varies depending on what I'm doing and how fast I'm typing.
I did something similar, but I mapped it (on hold) to cmd + control + option + shift so it effectively becomes a new modifier key that I use to define shortcuts that will never clash with any existing shortcuts. I use it to launch / switch to specific apps, move windows, etc.
Oh my.... I never thought of this.
but then again, I use the side of my palm for holding control.