Yeah, a lot of companies seem to be missing at the moment. Not just Activision, but Sony and EA aren't there either. Granted, they could always come later, but it's something to keep in mind...Don't know about you lot, but it seems kinda suspicious that Acti isn't already in the initial list of attendees, when they've always showed up at E3 when it was available in some form. Always announced something there, so I'd be surprised if they didn't even show up there to announce something relatively smaller like one of On the Run's season passes (keeping in mind that N. Sane's Future Tense was announced there instead of Spyro Reignited).
As for Dragonborn, I could see him get in as a Mii costume. Looks to me like he'd get the Altair treatment.