I’m hijacking this thread here now 
The CheckMetadataHash signed extension and all the required integrations were merged as part of this pr. This means that chains can now get access to the generic ledger app by integrating the signed extension into their runtime. I have written a guide on how to integrate the signed extension etc into your runtime. It would be nice to get some feedback on the guide if there is something that can be improved to make it more easier to use this! Ty!
As promised, I also backported the pull request back to 1.1.0: Pull requests · paritytech/polkadot-sdk · GitHub
If you need to have this put onto crates.io, please comment here for which release you need this!
For the production runtimes of Polkadot/Kusama and all its system chains the plan is to integrate this change into 1.2.5 which should be released before end of june.