FTFY- added "Caliper" above, as the Rotor and Master do not follow a single standard. Also, handlebar clamp is not standard. Last time I was shopping for bars I bought the smaller diameter with a set of adapter shims, as it was 30% lower cost than buying the same bar with a diameter matching the stem on the bike.
Granted, it has gotten better.
For those who have dealt with this for long enough to learn the ropes it has become second-nature to take the steps to assure the right part is ordered. Still, for new people coming into the sport it can be frustrating having to wallow through all the minutiae just to make sure the part you receive is the part that will work.
But, this is veering further off topic. Which was that a standard battery spec could lead to several significant advantages for the OEMs and their customers.
Based upon reality, the complexities of the higher spec bicycle industry, and a long history of branded designs geared more toward finding their own way than collaboration, I won't be holding my breath waiting for this to happen. It is the nature of the beast.