Love to hear something may be in the works. But in my opinion, announcing during Epic's opening (and off-cycle from a D23) may come off as a bit desperate. Rather than stealing Universal's thunder, the business press (who loves a David vs. Goliath story) is just as likely to spin this as "Universal has Disney freaking out" and "Disney is dancing to Universal's beat" sort of framing. In fact, Disney is always more likely to get high-level press coverage for its parks vs. Universal, so a Disney announcement that week could just drive more coverage of Epic than it otherwise would have had as journalists cover the "theme park competition" angle.
And, really, rather than stealing attention from Epic, making a big announcement during Epic's week could mean Disney's big announcement is ignored, and has less impact.
In short, Disney shouldn't play this game. Let Epic have its moment. Don't draw attention to it, don't look like you're reacting. And announce your thing at Destination D23 once some of the bloom is off Epic's opening.