Argonians should be the only ones allowed to join the Dark Brotherhood.
As a fellow Argonian, I can only endorse this! Shadowscales forever!
But anyway, when I join (not if, it's a given I will) will depend on how far along I am when I find them. I hope the missions are even more humorous and clever as they were in Oblivion. Easily my favorite faction except for the sorry state the story line ended in. Less handholding is always good too. Though I don't recall it being THAT bad in Oblivion. One of the better constructed sets of quests.
If the Morag Tong are around, it would be truly epic to have some good old fashioned assassins quarrels to resolve.