Who should sit at the table? Well, there's Assad, for sure. The opposition is about half and half religious and non-religious groups. On the religious side there are al-Qaeda and non-al-Qaeda groups. What about "not negotiating with terrorists"? We can't exculde them because Assad would not be able to sit at the table. But might be a good idea to seat some representatives of the non-al-Qaeda Salafist factions.
AQ has a global agenda, its Global Narrative. The others, mostly indigenous, seem to be seeking Shariah, of their own definition, solely within Syria and without immediate threat to the United States.
Barring AQ from the talks might help isolate them on the ground. And the peoople of Syria will receive a clear message: AQ is not an option. Peace in Syria is dependent upon Syrians and we have to hope they see al-Qaeda as just as much a threat to them as it is to the rest of the world.