I've been checking for a SP CLI for my Double Cash card and finally the magic language appeared on Citi's website. Limit instantly went from $2000 to $3500. Still one of my lower limit cards, but I'll definitely take it. I hear that the Double Cash card has notoriously low limits.
For data point information, I applied for the card at the end of December 2015, so it hasn't really been six months since approval. Also, my scores are mid-700s and utilization is 5% or so.