That's generally the expectation right now. We simply don't have the bandwidth in Behemoth Designers to make a new keystone at this time, and the tradeoff to do so would cost us more normal behemoths. Additionally when evaluating our time between a new Radiant Omnicell, and a second Legendary, we opted to spend that time and energy on the Omnicell, and we think you're going to love what it is.
I've been thinking very hard about reasons to play Radiant escalation, it's definitely a problem top of my mind in understanding it's purpose within Dauntless. For many though, there's also just a desire to complete the set, to have a full suite of Escalations. There are still many questions to answer, but we're early in the process.