The speechcraft skill has always had a rather lacklustre implementation in previous games.

Morrowind only let you admire, intimidate, taunt or bribe anyone you were trying to talk to.
Oblivion seemed to think you were bi-polar, to go from joking and admiring someone to making threats in under a minute. It didn’t matter who you were talking to, they all accepted a bribe and were happy with it.
Fallout’s speech skill was the most diverse, but there were only specific scripted events that it could ever be used in, also it doesn’t work with the ‘learn by doing’ style of TES skills.

Something is needed to let you interact with the people of Skyrim without making you look crazy (unless that’s what you’re going for)
Since it seems speechcraft is a going cross-classes skill, it should be equally accessible to everyone, with some interactions that are aided by your knowledge of other topics, not only how convincing a speaker you are.

There should be options of dialogue that actually makes sense for different characters to use, gaining different responses from different kinds of people

Something like:
Friendly: (speechcraft based) [works on most people] ask them about their day, tell a joke, make some sort of connection.
Knowledgeable: (Speechcraft modified by magic skills) [bonus against scholars and mages] prove that you know a thing or two, and can back it up if the need arises.
Threatening: (modified by combat skills) [bonus against fighters] you think you’re tough, well go on, try something.
Inspiring: (modified by reputation) [works on most people] you rally those on your side, inspiring them in a time of need.
Smoothtalker(thanks SyphuuR): (modified by stealth skills) [works better on shady types] appeal to their lack of morals to side in your favour.

You should be able you try and persuade someone at any time, bringing up a new set of options and hopefully some indication of what sort of action the person it likely to respond to.

Scenario: you are ambushed by bandits on the road they want your money do you;
Friendly: say that none of this is necessary, and try to talk them into letting you go?
Knowledgeable: tell them that they really don’t want to be making threats at a wizard that’s standing so close to them?
Threatening: smile a knowing smile and just start cracking your knuckles?
Inspiring: tell them why should work for you instead?
Smoothtalker: tell them about the 'caravan' coming down the road that is ripe for the picking.


Or do you just start crying and hand over everything you own.
Reactions should go from getting bonus fight time while some of them run away, to full rout or some siding with you, to them attacking with greater conviction if you are unsuccessful.

Also it goes without saying that people should react differently to bribes depending on wealth and status, and that they should not be universally accepted.

That was the only realistic thing about it.

Not when a baron will be equally as happy with my 500gp bribe as the beggar, and that I only get an extra 10 disposition out of either of them

I wonder how its going to work with levelling, unless you seek out specific Speechcraft quests wouldn't every character use Speechcraft just as often, I mean the only alternative would be a charm spell, or maybe you steal information from a locked desk or threaten with your drawn sword.

But I prefer the scripted Fallout/Knight of the Old Republic lie/persuade/joke events rather than the Morrowind spreadsheet system or the INSANE Oblivion nonsense.

have an option to put your underwear on your head. who could seriously not laugh to that?

For stealth you could have sly / smoothtalker