I'm working on a proof of concept for this. I've put together a few adapters using the connector shell and contacts from dead batteries to plug into a modified DeWalt battery, so I've got the power supply side of it figured out. That's the easy part though... I don't have experience modeling for 3D printing, or access to a 3d printer, so that's going to take some work. And pretty much all lithium tool batteries have extra contacts for thermal sensor and some form of communication with the battery's PCB.

So far the driving force for this project has been an occasional need to run older tools with discontinued/unavailable (usually NiCad) batteries for short periods of time in a relatively controlled test environment, so I haven't yet bothered with the thermal protection circuit (which the tools may not have originally supported). In order to actually use the tools as tools I'll need to have some kind of controller in the adapter to monitor the battery charge level and temperature to make sure the battery isn't being overdischarged. This is handled by a built-in controller in modern tools but I haven't tested how they interoperate with onboard PCBs in different batteries.

Side note: I've been surprised learning about how much technology is in modern battery-operated power tools. There's a circuit board in the handle of pretty much every drill that communicates with the battery and trigger and runs the motor. A lot of them are potted in epoxy but sometimes I've spotted an Atmel chip in there.

There is actually a consortium like this, but unfortunately most of the brands involved are pretty niche. The only two I'd ever buy from it are Mafell and Metabo.

https://www.cordless-alliance-system.com/