These Chinese auto GL are all high velocity 40x53 for export. And we have seen these in action in Jemen and Iraq. But its 13kg unloaded, with the addition of Airburst kit weight grows 2.8kg further, 

''This air-blast kit mainly includes OS23 simple fire control and muzzle fuze binding device. The weight of the kit is less than 2.8 kg, adopting a method of timing based on rotating number. The fire control calculates the number of rotations required for the grenade to fly above the target based on the results of laser ranging, and then binds it to the fuze. When the grenade flies to the bound number of rotations, it is located at the top of the target, and the fragment would hit the hidden target into a hornet’s nest.''

Airburst kit .

But even domestic 35mm version has quite a kick

YouTube

PLA?? ??? ?? 11???????? China QLU-11 sniper grenade launcher

PLA?? ??? ?? 11???????? China QLU-11 sniper grenade launcher - YouTube ...

https://www.youtube.com/watch?v=uGvOXFsZCFI

YouTube

Shaped Charge grenades for the NORINCO QLU-11/LG-5 sniper 40mm grenade launcher.

Shaped Charge grenades for the NORINCO QLU-11/LG-5 sniper 40mm grenade launcher. https://thedeaddistrict.blogspot.com/2020/11/shaped-charge-grenades-for-qlu-...

Mr. T (MrT4) said:

These Chinese auto GL are all high velocity 40x53 for export. And we have seen these in action in Jemen and Iraq. But its 13kg unloaded, with the addition of Airburst kit weight grows 2.8kg further

Or just settle for 16 kg and go with the AGS 30?

https://modernfirearms.net/en/grenade-launchers/russia-grenade-launchers/ags-30-eng/

I also remember long ago seeing a picture in a International defence Review of a 30x29B grenade launcher which was a salvaged AGS 17 barrel on a scaled up Ithaca shotgun made somewhere in central america. No one dared fire it but it looked rather like the China Lake Grenade launcher. 

The Czech RAG-30 has been marketed for many years but I don't know if it's found any buyers. 

Anyone has the chamber pressures for MV 40x46mm or is it 40x51mm? 

In 40x46 mm LV, the "low pressure" chamber is around 20 MPa, and proof pressure is 23.5 MPa if I remember well.

A recoilless system springs to mind

Or maybe a modern day "PIAT" in 40x53 with airburst capabilities?

Might be a bit inaccurate due to the pre-shot-recoil, but at this modern day, counter-rotating gyroscopes should be a possibility.

Spin them up by touching the trigger, and brake them by releasing the trigger.

With the advent of options like 40mm pike and weaponized drones small enough to be used at squad level, it seems like a solution in search of a problem.  Things really are going to get very lethal very quickly over the next few decades.

Drones will be jammed by ir-smoke and lasers and other counter-measures.

If a nuclear nation is attacked by another nation, that is overwhelming them by weaponized drones, they may get nuked. If they attack with autonomous weaponized drones, they WILL get nuked.

Fully autonomous recon-drones will probably be accepted, but jamming will probably hinder live communication of images.

And that  means personnel will have to be close to the action, and possibly do a lot of the fire-fighting themselves.

Of course, that is in a major international war. In smaller regional wars, and civil-wars, humans will do most of the fighting, unless fighting against a major power. Like when Turkey used Aserbadsjan as a proxy against Armenia. 

One of the interesting things about 6.8 is its potential effect on HE weapon systems. 

Given the ~12lb weight of the 6.8 rifles once the smart optic is factored in, adding a ~3lb underbarrel grenade launcher would bring the weapon weight to 15lbs - about the same as the Milkor M32 with optic. That means that the collective weight should be high enough to fire Medium Velocity grenades without any need for a recoil dampening system. And the laser range finder and ballistic calculator of the NGSW FCU already provides most of the raw materials for a grenade launcher FCU...

On the flipside, by having a 6.8 LMG at the squad level, theres suddenly much less need for a GPMG 'weapons squad.' This offers the tantalizing prospect of reconfiguring the Weapons Squad from GMPG's to HE slingers - either an Airburst AGS-30 type system, the Imortar 60mm with FCU, or Carl Gustav's with airburst / guided rounds.