I don't have the means to develop the idea, but I've long imagined that a primer booster would be a useful innovation. First, we should understand that powders can have non-linear burn rates. They're "slow" or "fast" in burn rate, but they can also increase and decrease in burn rate through the combustion cycle. Progressive (increasing) burn rates are usually achieved through deterrent coatings on ball powders or surface-area features like perforations through extruded powders. As the deterrent coating burns off, higher energy cores are exposed and combustion gas production increases. As the extruded grain burns from the inside-out, the surface area undergoing combustion increases, accelerating the rate of gas production. Progressive burn rates are valuable to increased bullet velocities because they can avoid exceeding pressure maximums shortly after initial ignition, but then ramp-up gas production once the bullet has moved some distance down the bore allowing for more space for the gas to expand into. The challenge, particularly with deterrent-coated ball powders is ensuring a positive ignition and start to the combustion, especially when the case is large in diameter and even more so when it is deep and some of the powder is a good distance from the primer.
Using a small amount of an undeterred or fast burn rate powder blended with the more progressive powder could help with ignition. It would also make the burn-rate more digressive. It would be difficult to pack the increase in pressure into the combustion timeline before the progressive powder reached peak pressure.
Arranging the powder in the case is another possibility. If you've ever seen different colors of sand layered in a glass bottle, you get the idea. Cases would have to be full to prevent mixing. Another similar concept would use propellant shapes and textures to maintain the arrangement. If you've ever used Alliant Steel, you know that propellant flakes can be pretty large. Imagine stacking a large flake or pellet over the primer and then filling the case with a more granular propellant.
I imagine using some kind of primer booster could negate the need for large primers and for magnum primers and for differences between pistol and rifle primers except with regard to their ability to handle pressure. Perhaps primers could even be shrunk or primer mixtures reduced. If a primer could be reduced enough, it could even become non-hazardous and avoid classification as an explosive. The boosters would be regulated as explosive like propellants, but it would be far easier and less costly to produce what would amount to powder flakes than it would be to produce boxer-type primers.
If primers could be much wimpier than they are today, it would be no problem for primer factories to spring up anywhere and everywhere.