Is there an advantage to combining trim function with yoke? SUMMARY: What if the yoke didn't require constant pressure, as is the case with the current &quot;trim&quot; function?
In all cases that I know of, airplanes have had the yoke (which you need to apply constant pressure on) and trim (which you don't) separate. The yoke is used to short inputs, such as a roll or a pitch down, and the trim is used to maintain the aircraft in a specific attitude, given the changing nature of center of lift and gravity.
But I do not understand why it is necessary for them to be separate. Trim can do (almost) everything a yoke can. Would it be a good idea to combine the two?
Some advantages:

simplification
Safety; fast reaction to sudden trim changes (such as part of wing or empennage breaking off)

Some drawbacks:

trim does not center itself, so there's that inconvenience
increase chance of wild maneuvers if left unattended while deflected
I think you misunderstand what the purpose of trim is, which is to change the attitude of static stability.
The yoke (or stick) is the primary flight control. Virtually all changes in attitude will originate here, and any temporary changes also end here. If you take your hand off, the plane returns to the original attitude.
When you want to make a permanent change, you set the new attitude using the yoke (or stick) and then trim until the required pressure goes away. When you take your hand off the yoke (or stick), the plane remains in the new attitude.
Some planes do have an elevator trim control on the yoke (or stick) to make things easier on the pilot, but this doesn’t change how it is used. Some planes also have rudder and aileron trim controls; I’ve never seen those on a yoke (or stick), but I’m sure someone, somewhere has tried it.