I just realized that I never posted about our “solution” to the spell-identification timing weirdness introduced in Xanathar’s Guide to Everything.
Our solution is that you can optionally state that you’re casting “a mysterious spell” instead of the spell name. Both DM (NPCs) and players (PCs and henches) can do this. If you do, anyone who wants to try to identify it can use a reaction to try (int check vs 15+level, adv if is own class list), if you don’t, the spell is obvious to all.
Because XGE introduced that you need to use a reaction to identify what spell someone is casting. And countering is also a reaction, and you only get one reaction per turn, so there are situations where this Really Matters.
And most of the time it doesn’t.
When designing house rules, it’s often a good idea to try to cut down on ways players can “play the game wrongly”. (To be weighed against the benefits that a rule can bring—y’all know me, I love rules.)
Introducing “mysterious spells” helped solve all those weird timing issues and made the spell identification rules an optional benefit to PCs and NPCs as opposed to a chore to slow down the game when it doesn’t matter.
Making the spell “mysterious” doesn’t cost anything, it’s just a free, optional cloak, and it’s always better but it’s such a drag so we usually only do it rarely. But when it matters it matters.