I think lasers are a little far fetched, at least for the moment, but are worth attempting to develop. When solid state batteries come around, it might become possible to have an emitter+power package with a few shots, or few seconds worth of firing, weigh in the 3-5lb range, with the battery in a backpack and the emitter as a rifle handguard type attachment.

As you said, airburst/range burst grenade weapons were a failure. To have them be a success against drones, you'd have to solve the lead-the-target problem rifles have, with a single, much slower, projectile and have a smart round that auto-detonates when it is close enough to the drone. The blast radius makes up some on the targeting front, but I'd suspect you have a 3-5m effective kill radius at best on a grenade delivery sized drone.

It would likely be possible to build a specific anti-drone round to limit collateral damage, but you probably reduce its effective range and effectiveness at the same time to do so.

So the targeting system would have to acquire the drone, figure out the lead, on something potentially moving erratically at 15-20m/s to fire a ~700fps slug with the trajectory of a thrown stone, and take the users reflex/fire time into account, to set the detonation timer.

With the projectile velocity and drop, speed of the drone, out past 200m you are going to have a very low hit rate even on drones flying in straight lines. I'd guess the projectile drop at 200m is around 10 feet and every 25m after that is a couple more feet, and by 300m its probably 5' plus and travel time to 300m is probably two seconds or more. Even with a 5m kill radius any little change in drone direction or velocity is going to result in a miss, and it may just miss because I have no idea what the MoA on an xm25 is. A ten inch circle at 200m won't matter much on the stationary target at 200m, but if you are trying to hit a little drone moving 40mph at 200m, its a bigger deal. Follow up shots will be fairly slow because of the recoil. You might be able to stack a few near-hits to bring one down. But, and there are some big buts.

You, the user, have to figure out if it is safe to fire before you pull the trigger, because there is a ~15m guaranteed injury zone around the blast, a good chance of serious injury at 50m, and potential to cause injury out to 200m within the detonation radius, based on the regular xm25 air detonation round. You aren't in cover, arcing the round behind the cover someone else is behind, a static distance away.

It's probably fine for guys in a trench on the front line but the system is going to be dangerous to the user and those near them inside of 100m, or anywhere within 100-200m of the detonation, since you are bursting projectiles up in the air instead of mostly in or behind cover. Which limits its effectiveness close in even if you are in a trench w/ only foes in front of you, and the slow velocity, high drop rate and speed of your target limits the distance you are likely to hit it at. So there is a very limited window of effectiveness as far as how close you can shoot a drone, and how far you can shoot a drone, even if you don't have to worry about collateral damage. There were all sorts of RoE during GWoT for discharge of underbarrel and thrown grenades for infantry to prevent collateral damage in urban and semi-urban environments.

Basically trying to defend yourself or anything that isn't on the front lines, popping off a grenade 10-40m off the ground may frequently cause more damage than good against little suicide drones. Urban environments, multiple squads on patrol behind the front lines, etc, who knows what you might hit, even if the drone is detected far enough away from you personally.