The average soldier isn't going to be able to use directed energy weapons in the same way as a projectile. The energy requirements are far too high and the source of it too bulky. So far most of the projected experiments are vehicle mounted. Even man packing a small generator doesn't happen in today's combat environment. It's the exact same problem we face with the exoskeleton suits. We can't and don't have a good energy source. What we do is often as much a danger to the operator as the weapon, same as gasoline was to the Sherman tank.
What a directed energy weapon CAN do, tho, is destroy a soldier's vision and make him a casualty on the battlefield instantly. That's exactly the same thing as shining a laser at an airline pilot. We are already restricting and controlling those because of their irresponsible use, and it's already considered a terrorist weapon. It then begs the question how does it fit into the Laws of Land Warfare - if the hollow point bullet is considered unethical because it caused too much maiming in the late 1800's, then how do we ethically accept directed energy weapons that blind or burn? Let's not forget the continuing drama about using napalm or phosphorous - if it burns, then what difference does it make if it's caused by pyrotechnics or light packets?
Because of that international debate and the ongoing misuse of consumer items, I do see that gunpowder powered projectiles can and will make the next step into plastic cased telescoped ammo. One reason is that it's working out - while caseless itself isn't reportedly all that good, even from the HK designers view, plastic cased LSAT ammo and the weapons that use it continue to be funded by the US Gov, with SOCOM involved in testing now. There are enough prototype weapons to equip a battalion of soldiers, rifles and machine guns, for field exercises. That implies blank ammunition may already be on the shelf, too.
A 40% increase in the ammo a soldier can carry, plus no brass casings, means not only a more effective combat force, but also a significant logistics savings not wasting time and effort to salvage brass for resale. And the political advantage for some is that the empty cases don't fall into the "enemy's" hands - American citizens who can reload.
It would be extremely simple to restrict supply to ONLY government users, too. "National Security" could be invoked, which means agents and soldiers wouldn't see the same ammo coming back at them. Many other countries outlaw the use of military issue cartridges, some so much they outlaws any other country's, too.
As long as we have power cables attached to directed energy weapons, and a trailer generating the power, we won't see them in the hands of soldiers. high energy lasers are already problematic from a number of political angles, so that leaves improved cartridges - which haven't radically changed in 100 years.
But, there is another problem. We've already transitioned into the 4th generation of warfare - Low Intensity Conflict, or terrorism. Large scale land warfare isn't much on the table, because of the costs to governments and how much more tightly the world economy is connected. We've moved from large nation states battling each other to small intense groups based on morals and ethics challenging the nation states, and what kind of weapon is now entirely flexible. We fight a running battle with hackers, arsonists, bombers, Mall shooters, etc. YOU and I aren't going to get a directed energy weapon, or for that matter, a new issue caseless rifle to carry around as our PDW shopping in the city. We're going to continue to carry what we know works - a handgun, and keep a rifle an arm's reach away. That's what is really happening in today's world. Upgun to arming rebels who fight a normal war of battlelines and holding territory and things revert to traditional warfare methods, and those proponents can demonstrate some very harsh reductions in their opponents combat effectiveness. It's the inexperienced who don't know better and attempt it.
