Separate Main/Monitor Output Graphic EQ stored by preset

What do you mean by "global"? You can save any Output configuration as a preset, and this will include the EQ settings you decide.
Of course a 3-band EQ is less versatile and effective than a graphic EQ, but IIGYR they are not more "global" than how a graphic EQ would be.
Am I missing something?

OK, got it

Mhhh... What you're suggesting would go against the design.

I am still puzzled by "it's very common that you have to tweak EQ to get the sound right in the main outputs, but then you mess up the monitor output (using a guitar cabinet) and also the other way around". These corrections have to be made in the rig, not at the output.

The Output EQs are meant to act on\correct the device after the Profiler (typically an active cab), or the cab\room combination. You are supposed to be in one room and use a (combination of) cab(s) per time, and it would make no sense to change the output EQ on a per-rig basis. There are the tonestack, the Definition and Clarity parameters in the Amp section, and the stomp and fx EQs for the purpose you're considering. Also, choosing the right profile plays an important role in the basic tone definition. Usually several profiles are released for the same amp\cab\mic combination, which differ for the basic tone\EQ.

The only reason this could be useful is if the 6 slots are already in use and you want to use more EQ, but this would IMO fall under the general case of "we need more slots for the fx"

The problem you are running into is you're essentially creating two sets of sounds, and neither are balanced. Your sound guy will manage the sound in the room, and it doesn't matter how high (or low) you set the treble or bass, they're going to set it to fix what sounds good to their ears. The other problem with programming in sounds for your cab vs. sounds for a PA/studio is that they inherently sound different. You wouldn't mix half of your album on $15 radio shack desktop speakers and then the other half on quality studio monitors, and then wonder why your album doesn't sound right. Same goes with the Kemper. Stick to making your patches on one device, then you can compensate for other outputs, just like a car stereo has EQ settings to adjust how the song sounds in a car.

What I would recommend doing is this:

• Obtain a studio monitor if you don't have one already. You don't really need two, just one will suffice, and it doesn't even need to be that high of a quality monitor. Headphones, your standard guitar cab, etc. - they won't work for this. If you need to borrow one, fine, but I'd certainly recommend at least having one around. You could do this with your guitar cab instead and inverse the process, but then you're making a sound that sounds good to you, and the audience/studio/whatever is less of a priority. Maybe that doesn't matter to you, but it does matter for the tens, or hundreds, or thousands of people listening to your playing. And, last time I checked, if an audience member doesn't like what they hear, they're not going to support you and/or your band.
• Set all of your global EQs flat, dial in your clean sense for your guitar, and leave it alone.
• Sit down and go through every sound you use. Dial in what sounds good at a loud volume (because what your ear hears loud, at a live performance, sounds different than at bedroom levels). Make changes to the EQ in the stack, add post-EQs if you want, and mess around with the cab block being used for those profiles. Those are going to make the biggest impact, and this will be how it sounds through the PA or at a mixing desk in a studio. I would suggest trying to find a really good cab (TillS's are really nice) and use it globally (locked) that matches what your actual guitar cab (i.e. if you're using a Marshall 1960, use a Marshall 1960 cab on your sound). If not, you're going to get drastic EQ differences where one profile is going to sound very bassy through the PA but not so much through the cab, and others that will bite your head off through the PA but fine on stage. You're going to hear a very different sound coming from your cab vs. coming from the mains if you're using different cab types. The cab makes a huge difference in your tone. Also, by locking your cab, you're not worrying about the mic either (because all mics capture different frequency ranges), since that is a part of the profiled cab tone.
• Now that this is complete and all of your patches have been saved, disconnect the monitor, make a backup (because you should!), and plug in your guitar cab. At this point, your cab will probably sound either very muddy, or very bright. If you used the same type of cab in your cab block as you use live, there's a possibility that it may be spot on, but unlikely. NOW (AND ONLY NOW) you can tweak your monitor out's EQ to taste.

After that's done, all of your profiles should be fairly even, balanced, and properly EQ'd. Your main out should be completely flat, and your monitor out may have some EQ on it. If you want to adjust your monitor further, go to town. But leave your mains all flat. If you show up to the venue and it doesn't sound right through PA, then you can adjust the main out EQ and you're golden.

I think the consensus at Kemper HQ is that the differences with cab on for FOH and cab off for monitor out use with a guitar cab are not huge enough to not be able to be compensated for with the output EQ in its current state.