Morkus from Orkus
If it were everyone, it would say everyone. All the NPCs are different someones. The word someone is not enough to carve out an exception for PCs. Not when literally everything in every social skill and the social interaction sections in both the PHB and DMG involve use against NPCs.The rules just say "someone", so it's clearly any character in the game world. About the effects, see below.
Sure. The DM gets to decide auto success/failure or in doubt for his NPCs just the same as the player does for his PC.Exactly, which means that there is no prescribed effect for success or failure whether on NPC or PC (and used by NPCs or PCs, although the PH speaks to players, clearly NPCs have social skills too), which means that it does not have prescriptive valus on anyone, whether PC or NPC. It's just that the DM interpret what it does on an NPC (which he controls) just as a player interprets what it does on a PC (which he controls).
Yeah. Circumstances change everything. The NPC pet store clerk will likely give in to whatever the PCs demand with no roll. The hulking mercenary all by himself might be intimidated enough to back away, sword on hand, letting the part know that he won't stop them, but if they drop to take his stuff or do anything that the fight is on. That same mercenary with 8 of his buddies might be an auto failure on the part of the PCs to intimidate. Why would the be intimidated by some punks that they outnumber? And of course, as you point out, the intimidation doesn't mean that the plotting stops.I will add to this that the effect might, in every case, be partial depending on the circumstances, for example the kobold intimidated in sitting quietly might do it, or not, but he might also do it and plot something else as soon as the intimidator is away, etc.