For Plasma 6:
The idea is simple. Be able to make 24px icons work in Plasma.
Reason: it's more about the numbers. Nothing special. But it also sounds more reasonable as a number in the set of sizes we use for plasma (16,32,48,64...) over 22. What a random number...
How would that work? If that ever happens, 22 icons should still work, because Breeze and Oxygen do not include 24px icons at the moment. Breeze could have some day, but Oxygen seems more challenging. That would mean, that "support" for 22 would still exist but support for 24 may be added. So people could either make 22 or 24 icons and both could work. I don't know a better "workaround", if that is one anyway.
This could be "added" in the new frameworks for (6). Write down whatever you like if you have an interest.