It doesn't make sense anymore. And as we move further away from physical media (sadface), it'll make even less sense. E3 was basically for retailers and such - and they're not going to be selling the games anymore.
Even things like PAX don't make much sense (from the Developer/Publisher side of things). Why invest all the time and money to travel/rent space/staff/and set up demos that only a limited amount of people can play when you can upload Youtube videos yourself and free demos that everyone can play?
In a time where if you wanted folks to play a demo of Ocarina of Time, you needed special hardware and had limited ways to distribute the software, it makes sense. Today? meh.
I see one of two options going forward. One, we go back to CES (is CES still a thing? I dunno) where it's general consumer electronics. Put the Nintendo next to the refrigerator with WiFi cameras installed. Not really a good format, but more likley to survive. Or, a total gaming expo. Like PAXxGenCon - Table Top, RPG, Card Games, and Video Games. Tournaments, vendors, devs and publishers...
But something only for Devs and Pubs direct to Industry Resellers? Naw, it's dead dog.