Ran out of time to respond, will look over the next page later
Why do every body want to scry an enemy?
Pick a mouse, a familliar or whatever small creature you can find and send it in. Scry it as it invisibly scurry around the castle, fort, cave or whatever and as you see enemies, you now have seen them (and scry them later). You can even now teleport into the place as you now have seen it.
You mean you can safely get within 100 feet? That is how close you need to be to see through your familiar's eyes (also, this is not a thing Sorcerers can natively do, again.)
Oh wait, you just want to use two concentration spells to follow an invisible mouse, getting ten minutes of scrying footage... so basically the same thing but without the wisdom save.
Also, afb, but I think having seen a place through scrying still leads to problems teleporting in, and anti-teleportation wards are more common than anti-scrying wards for high-level enemies (otherwise you could lead an army into the enemy's bedroom, which seems like the type of oversight a serious threat doesn't ignore,)
You can learn about some of the dead inhabitants and use contact other plane and question them about the strength and weaknesses of the place. After a few days you almost know the place as good as the inhabitants. Teleport into an empty (or unused or not often entered) store room. Use Arcane eye, and finish the scrying and get the info you need.
Arcane eye, yet another wizard exclusive spell.
Man, for how obsolete they are, they sure seem necessary to all of your planning to make them obsolete.
Also, Contact Other Plane has two, small, minor problems. 1) It does not say you can contact specific dead mortals, but an "extraplanar intelligence" yes, a long-dead sage is an example, but it is a grey area. 2) There is nothing in the spell that says the answers have to be truthful. So, if you ask a question of a dead cultist about their cult leader, they can fully lie to you about what you want to know. Also, since it needs to be stated again. Wizard and Warlock only. Sorcerer can't cast this spell. So the sorcerer can't use this to make the Wizard obsolete.
Hell, a high level rogue with expertise in sneaking can do this on his own without getting caught. Getting info is not something that hard to do.
If your 15th level threat is safe enough to send a party member in just to gather information... why aren't they just completing the mission? If I can reliably and safely have the Rogue sneak in, that castle is going to be coming down, or burning to the ground.
Assuming that the Rogue can just scout the entire place with impunity makes me wonder why this is a threat. Poison all the food, foul the water, burn the castle, steal the weapons while they sleep. You will stroll through the place while they are dead, dying, or helpless. Information is the last thing you need in that scenario. You've already won.
Once you know what you're up against, change your spell list as you wish since now you can do it. Before the wizard disappeared, you only needed a wizard, now you need either a bard with the right secret or a warlock. But this is hardly a problem now isn't it? Since most groups that I am aware of are usually 5 or 4 with an NPC...
Ah, an acknowledgement that the wizard was the one doing all this.
So, the sorcerer has made the Wizard obsolete.... as long as the Bard has used their magical secrets to gain the wizard's scrying spells, or you get a warlock.... wouldn't that make the Bard or the Warlock the one making the Wizard obsolete?
Maybe we should abolish them, instead of the Sorcerer?
Nah, this is all because the sorcerer is supremely powerful with their perfect information given to them by the rest of the party. They are the true problem.
I still think that people are generally underestimating the potential impact of Spell Versatility.
This is definitely not a "retraining rule", because of the fact that you can swap one spell every single long rest.
This is a challenge-bypass rule. Just because it is limited to ONE spell and requires at least one long rest of waiting, it doesn't make it trivial. You are not really going to exploit this rule much if you just change one combat spell into another (which is what 90% of the people seem to think about), but you ARE going to exploit it when you know tomorrow you have a long trip ahead that you can bypass by flying or teleporting, and next day you need to breathe underwater, and next day you need to telepathically contact someone very far away, and next day you need party invisibility to sneak into the castle, and next day you need to reveal a key clue with a clairvoyance and so on... Sure if you need ALL of these tomorrow, maybe Spell Versatility won't help you.
The game already has too many spells designed to bypass specific non-combat challenges. Those spells are designed for people who dislike non-combat challenges or having to come up with creative ways to solve problems, where "creative" means at least not just press-a-button spells. Those spells DO get in the way of other players who maybe want to have some fun thinking about how to beat a challenge instead of pressing a button, even if it requires to wait until tomorrow, and it can actually spoil other player's character builds.
The issue with this though is that there are no other ways to do some of those challenges.
If you need to telepathically contact someone far away, there is a single spell that does that. Two if you count the sending spell. If you don't have that spell, you cannot succeed. Teleporting without a teleportation circle? Literally a single spell, two if you count going to a different plane via plane shift (which has it's own problems)
The fact of the matter is that if you design a series of encounters where having a single spell counters the encounter, and you speciifically map them to spells the sorcerer knows... then yes, this ends up powerful. But, you have also set up a scenario where they were going to be stymied or stuck without those spells, with no other way through. Is there another way through? Then why are we waiting 24 hours for the sorcerer to sleep for the day?