Does having different sized coins strike you as an inconvenience?
Why does a feature that can be used by anyone, regardless of disability, strike you as "inconvenient for almost everybody"?
What, exactly, is inconvenient about having notes be different sizes?
This has never been my experience. What is the challenge?
I keep them in order, with €5s in the front.
For my side, even if I did agree with your preference, I am perfectly willing to deal with the incredible hardship of slightly different sized notes in my wallet in exchange for a society where disabled people need not fear being ripped off.
https://www.nbcdfw.com/news/local/counterfeit-currency-warni...
I believe the US made washing much harder with other techniques because of this in recent years.
It's clearly not a solution, and it seems like it's a suggestion that can only come from a place of "but we've always done it this way" without experiencing a world without the problem.
Even if 5s and 10s are the only ones mixed together, I still have to look for a number. In every other currency you just… immediately take the right one.
That's not even taking into account that wallets are getting smaller and smaller as people need to bring them less. So adding dividers would be like acquiring George Costanza's wallet.
Hell, if they're different size you can even feel the value of a loose note in your pocket.