Swarmkeeper
Hero
And yet nothing I said there was wrong.
"So is every teleport spell, fireball, firebolt, and so on." - Barring some other specific rule changing things, these can only be cast on your turn.
"The purpose of Ready is to interrupt the other person's turn and then cast a spell out of turn as an exception to the rules." - This is true. The purpose of Ready is to provide a specific rule to allow the casting a spell(or other action) out of turn.
"I'd allow Misty Step, since it seems silly not to." - This is also true.
"I just don't see a good reason why it shouldn't be able to be readied." - And another truth.
Do you have a good reason other than what it says about casting times? Because that doesn't seem like a good reason to deny a spell to me.
Yes, we are all speaking the truth 100% if the time if we own those truths.
Of course, depends if you are talking in the context of RAW or not.
Please explain how, by RAW, you can't cast teleport, fireball, or firebolt as readied actions.