So I've been planning to institute a new rule to make Proficiency more meaningful, because I don't like that the dumb barbarian can roll higher on History than the very smart wizard with a bit of luck, or that the very smart wizard has a much higher Religion roll than the cleric because the cleric's Intelligence isn't as high. I'm thinking on a case by case basis, characters can only attempt a check if they have proficiency in the relevant skill. Obviously checks everyone makes routinely, like Athletics or Perception, wouldn't be subject to this rule. Some would be variable: foraging for food might not require Survival proficiency, but tracking an animal probably would. And knowledge skills like History, Nature, and Religion would always require proficiency—and proficiency might often guarantee success.

Also, if I hear one of my players say "Can I Insight check him?" one more time, I'm gonna eat my DM screen. So I'm planning to treat Insight like Perception, giving each character a passive Insight and having sneaky NPCs roll Deception with that as the DC. That way, I can tell them "you sense that they're not telling the whole truth" without the awkward, character-breaking check.

What do you guys think?

I'm all for any rules which reduce game-pausing rolling. When I start DMing (bloody lockdown's put pay to my schemes) I'll want to get any passive effects (like deception, perception, etc) out of the way and not be something for players to ask for. I'll also be enforcing a "no asking for rolls" rule, where you describe what you're doing, and then I'll tell you what to roll for it. If they ask "can I roll to persuade", then I'll allow it, and the guard will look at them and wonder why they rolled a dice. Roleplay, not Roll-play!