It appears there is a souper precision bayonet attachment debuting at Modern Day Marine.
While I would love a quick fix for mounting a bayonet, the idea of attaching it to a free float rail doesn't exactly give me a warm fuzzy.
Bayonet lugs have always been affixed to the barrel, I'd imagine because the hold between the barrel nut and receiver are the most shock-resistant in terms of taking forward impacts and lateral slashes.
Curiosity got the best of me, so I dug out my OKC bayonet and took a look at it on the PredatOBR
As you can see, the hand guard is obviously too long to accommodate it, even if there were a lug on the gas block.
Removing the hand guard tells a different story though.
If you had a 20" barrel, or a shorter hand guard, it could accommodate a gas block with a bayonet lug machined into it.
The most interesting point in all of this, is the the Tranquilo muzzle brake actually mates up to the ring in the bayonet like an A2 flash hider. I would say that the threads would need a thread protector to keep them from getting damaged by accidental contact with the bayonet ring mount.
It appears that all that is needed is a gas block with a bayonet lug that's properly spaced for the Tranquilo brake.
I mean, I know the tOBR is deplorable. But a bayonet lug would make it
Extremely Deplorable