Dialog rscs have a few more attributes to configure the new dialog features added in A2, but it just complains (RPT error, not crash) about the missing ones and so you can add them easily enough. Sure someone will document them soon enough (I would, but I'm busy enough with other things!).
Objectives in the briefing.html have been replaced by scripted tasks, so you can now add and remove them during the mission (as well as select the current task and mark as completed and failed. This is a bit more versatile and a welcome addition. Not sure if the old-style objectives still work though, but I expect they do.