Being independent and self contained with control, in any environment, is always key to a confident performance.
The problem I see with this is if your guitar is being fed to the FOH desk then the FOH desk is sending you a full mix for your IEM how do you turn down the guitar level coming back from the FOH desk sent to you?
Having said that, the guitar volume control on the above is only for headphones BUT it doesn't turn down the FOH full mix back to you therefore making the guitar volume control request ????
The only way this could be successful is to ensure the FOH full mix excludes your guitar from 'your' full mix back to your KPA.
Sounds easy enough however, how many separate aux sends does an average desk have when you have at least 4 - 6 stage musicians wanting a tailored send to themselves.
Many future digital desks will I suspect however, the many analog desks being used in average venues today will not have many separate aux sends.
The above is a futureproof request maybe?
If I've missed something please let me know as I may not have fully understood the request.