While creating the power saver pedal I had a few people ask about the possibility of creating a solution for active pickups. This presents a couple of different challenges, opposed to a pedal perspective.

Active pickups generally use a 9V battery, some use 18V.
The circuit is usually enabled with a secondary connection on the input jack, so any time a cable is inserted, you are using battery power.

Having the pedal running with sleep mode has showed the attiny to use very little power.

How do you enable. or wake from sleep.
Signal, motion, tilt, button, lots of methods, I'd prefer just to listen for signal instead every 4? seconds, instead of a deep sleep, (waking on the pedal press). This may use more power, but I think with a reasonable rechargeable battery, you could recharge it comfortably at string change intervals. Power could also probably be disabled with the input jack as well.

If a jack was inserted, and no signal was heard in X seconds, turn off, sleep 4s, check for input.
If we have input turn back on.
Upto 8s seems a little bit of a lag time for a player. Up to 4s is still laggy, but I think would be tolerable for a wakeup in most situations.
Anytime you forget to unplug, it will save the power, just strum to re-activate, within 4s it will be back on.

Another question is the output of the pickups with and without power. Can we still 'pickup' an active pickup with the attiny?

With a secondary battery, what is the best way to recharge it?
A power bank and maybe a stereo switched jack, with a 1/4 to usb "creation" to route 5V to the power back through the input jack.

More time will tell.