well…, if there is 5 quarter notes in a bar than it is 5/4 not 5/6.
Seriously though, I understand the concept of what you call “irrational” meters. I just think this practice is unnecessarily confusing.
Classical time signatures are consistent with what’s inside the bar. Even if you hide all time signatures, you can still perform music as intended, because the number of notes and their grouping in the bar tell you the correct time.
Now, if you try doing it with your irrational time signatures, there will be no way telling which bar is which.
The solution is very simple. 5/6 should hold 5 quarter note sextuplets, marked as sextuplets, not as regular 5 quarter notes.