One suggestion is - if you are grappled, any hits the grappling creature gets against you are considered automatically critical and sneak attack definitely applies. Thoughts?
When I first read this, I thought "no way", but I was reading it as ANY grapple situation. But you're saying "hostage situations". So we're talking like, a rogue is backed into a corner by the PC's, holding a dagger to a hostage's throat. I would take it a bit further then what you propsed, in this scenario, and call it a readied coup de grace (even though the rules don't support this). I don't care how heroic you are, getting a perfectlyaimed dagger to the throat is gonna hurt.
In this situation, yeah, I would support this rule.
I read this as "any" grapple. Clarification?
Not any grapple. In my mind, it would be a grapple that requires at least 2 rounds of success (or an already immobilized hostage, such as someone tied up or paralyzed). Essentially, if the grappled character is still reasonably 'fighting', this doesn't work. If the grappled character is out of options except for trying to break the grapple, and fails, then it can be a 'hostage' situation.
Your suggestion makes some sense in the 'hostage situation'. However, it seems like it shouldn't be at all easy to get someone in a grapple like that. You basically have to have one hand free to attack while still keeping your opponent grappled. Maybe if you won the opposed grapple check by 10 or something you could do it. And then if your opponent survived the free critical hit they should get a bonus to escape the grapple on their next turn.