I'm assuming they ran out of ideas for Warframe or don't have anything prepared for the next big content update.
Soulframe in Tennocon doesn't seem to fit right, I'd say it feels like its affirmation that it isn't a waste of time. But I'm more concerned if they don't announce anything like they did with Duviri or Railjack before it was released, leading to speculation that there might be nothing big on the horizon to look forward to.