A timer would just force them to write better paraphrases. 
Funny that I'm in the minority. If not timers, they need to bring more challenging and "gamey" aspects to dialogue.
Either that or do something DAI did. One subtle feature I like is it is constantly autosaving during your conversations. Unless you manually save before dialogue, you're gonna have to live with the dialogue you pick.
Fair enough if thats your preference.
Personally I don't want dialogue turned into a mini game or to be challenging in anyway. Sure, challenging in terms of what to pick/what choice you make, but not mechanically.
And if I select an option and my character sais the complete opposite of what I wanted to say, I'm gonna reload, I'm set against any kind of feature that would stop me from reloading/redoing something. Shouldn't have to live with a paraphrasing fail, if they implemented some kind of live with your choice system then they better provide the full dialogue instead of a paraphrase.
Can you tell I'm annoyed by the paraphrases? 