The big question is what does it mean to attend "in principle ? Does that mean they actually plan on attending? Do they just wanna act like they are there but arent really there? However stating that i do think the Syrian gov should attend all talks. Its clear nothing is going to come of it without the Syrian gov.
The agreement to attend in principle merely reflects general agreement to attend such a conference. The conference's agenda has yet to be defined and acceptance in principle allows a party to back out if disagrees with the terms. For example, if the conference is about launching negotiations for a path forward, a party might attend. If, however, the agenda is defined with preconditions such as a party's yielding the possibility of having a role in a future government, the party could back out.
The anti-Assad movement has been insisting on tying diplomacy to President Assad's stepping down almost immediately. However, there is no agenda that has been created that calls for such an outcome required to pursue diplomacy and the anti-Assad movement lacks the battlefield position to make that a credible demand. Therefore, if that were a precondition for launching talks, the Assad regime would very likely reject that precondition, even if that meant there would be no negotiations. In the outside event that Russia and the U.S. insisted on such terms, the regime would probably choose not to participate in the conference. In contrast, pursuing a transition to post-Assad rule is, however, a legitimate aspect for negotiations.
At this time, I suspect that the Assad regime will attend the conference, if it is held, unless the kind of precondition I cited above is sought by Russia and the U.S. (cosponsors of the conference who will largely shape the agenda). The Assad regime is trying to restore international credibility and attending the talks serves that end.
That leaves the anti-Assad movement with a tough position. To date, that movement has insisted on a near immediate resignation by Assad. That is not going to happen. Whether that movement will attend the talks under such circumstances is an open question. I believe that it will, as well, as that movement is trying to bolster the case for receiving more outside arms. Its failure to attend could undermine prospects of increasing the level of support from outside states.
Having said that, the differences among the two parties to the sectarian conflict are very large. The battlefield position remains relatively close to a stalemate with neither party in imminent prospect of knocking out the other. If that were the case, the party on the brink of victory would choose to pursue the military solution to the end.
Nonetheless, the anti-Assad movement has adopted an attitude that it should be given what amounts to full authority over Syria's future. It sees itself as the inheritor of the future of post-Assad Syria. However, that demand is disproportionate to its actual on-the-ground position, which might even have eroded a little in recent weeks, so the Assad government is not going to accept such a starting point. The anti-Assad movement is also comprised of elements with widely diverging interests, and that might hobble its unity. As a result, even if the conference is held, it is highly unlikely that there will be a major breakthrough. The minimalist idea of reaching agreement to hold further talks and perhaps develop a modest agenda for those talks might be the most that is attainable. In the meantime, the battlefield will likely remain the major venue in which Syria's future is shaped and, unfortunately, barring a newfound respect for civilian welfare by one or both parties to the conflict, the terrible human toll will likely continue to mount.