I know there are some solutions already available, but there are caveats and particular bootloaders, etc.
What I wish I had is a simple device, preferably I2C so it doesn’t tie up anything, that I could write a timeout value to. If it counts down to zero without the number being changed, then it does a hard reset followed by doing absolutely nothing until it receives another count. The bootloader would be immune to it by design, as would any sketch that didn’t specifically program it. It would be nice if it had an LED that indicated that it has done at least one hard reset since being powered on or a readable indicator.