Average party gets two short rests a day. Not a big deal. It's funny though, it seems you do understand the concept of flexibility from just a couple of changes to selection. All of a sudden. When it's wizards being talked about instead of sorcerers.
Because unlike Sorcerers, they are completely limited in spell selection to what's in their book. A grand total across 20 levels of 44 spells, unless they get magic items. It matters a whole heck of a lot.
I am starting to wonder if you've ever played a Wizard in 5e? This is basic stuff you learn really quick if you play a wizard.
Okay, you seem to not understand what my problem was, and jumped immediately to snark and thinking that you somehow proved something. My confusion came from you sounding like you had no idea what you were talking about.
First off, I have always understood the concept of flexibility, even when talking about the sorcerer. I never even questioned it when applied to this wizard idea. I took and keep the stance of, if you feel like you need this for your game, go ahead.
Instead, I said this would remove the need for a wizard to scribe new spells. They would never
need to do so. And that the removal of that key part of the wizard identity would make it so WoTC is very unlikely to make your proposed rule as I understood it.
Your response was to say they would only be able to change spells this once per day (false, because short rests are an average of twice. So, you were wrong) and that the spell was not permanently in your spell book, so you would want to copy it anyways.
But, again I ask why?
Your response was to say that wizards are limited in the spells they can select for the day (after a long rest) by the spells in their spellbook. The 44 spells you mentioned. However, I am guessing you have forgotten that that is only partially true. Because a wizard only needs to memorize new spells to prepare, if they are changing them. If their spell book is destroyed, for example, they do not lose the ability to cast spells, they are simply stuck with their selection of spells that they had chosen for that day.
So, since you don't need to rememorize them from your spell book, and it is only an hour to get new spells, and following your own path of logic that a full day for a single spell is trivial, then the wizard would have full access to their entire spell list and have no need to write their spells down in their book. If a spell was so important and necessary that you wanted to have it available to easily swap in and out constantly, take it as one of those 44 spells on level up.
Of course, if it is so important that you want to have it every single day... don't. Because that is wasting space in your spell book. Since you would never need it in there.
P.S. I considered it possible that you meant that the wizard spell gained on the short rest had to come from your book, an explanation which would make your assertion make sense. But, re-reading your response, you clearly said that the spell would not "permanently" be in your spellbook, so you meant it to work the way I assumed.