Perhaps the analogy to a .30-06 wasn’t the best but I think it illustrates that whatever the military uses is going to be popular and available for a long, long time. CR123s were/are mostly used in tactical lights used by the military, LE, and to a smaller degree the civilian population of those who needed (or wanted) bright, compact lights. Obviously a CR123 is never going to be as “readily” available as a AAA or AA batteries that are used in a myriad of other devices but CR123s are still available at many hardware store, home centers, and even drug stores. For those of us on the platform, we’re buying likely buying in bulk anyway.
At this point and probably into the foreseeable future, CR123s are going to dominate the weapon light market. Given the situations where you are going to need a weapon and a light, my preference would be for the best light available regardless of the batteries it used. Of course, you can forego the weapon mounted light and just use a flashlight in your off hand. That would give you at lot more options for lights and battery platforms.