Even without Sony's presence, I'm looking forward to E3. On MS's end, we should be getting more news regarding Halo Infinite and Gears 5, and I'm hoping we at least get some kind of tease for the next-gen Xbox. Maybe a sizzle reel showing off some in-progress footage for some expected launch window titles. If the Xbox 4 is due out in Nov. 2020 and Sony will be absent from this E3, this would be MS's opportunity to knock it out of the park this year. I also hope they show off some new IPs, preferably single-player stuff.
Nintendo ought to have quite a lot in store at E3 as well. More details on Pokemon Sword & Shield and other games for the second half of the year are almost certain, and maybe we'll get some teasers or trailers for some 2020 titles as well. I'm hoping that we'll see the first teaser for Metroid Prime 4, and hopefully also an announcement for a Metroid Prime Trilogy HD.
I'm also looking forward to Bethesda's conference. Of all the major third-party studios, they seem to have the most interesting lineup of upcoming games.