Current widespread thinking is that Scorpio really needs to announce some system-seller games, and to surprise with something stellar and unique at E3, for MS to have a chance of Scorpio not being DOA this holiday.

They need an annoucement of:

• Halo 6 (would amass a lot of xbox360 gamers)
• A new Splinter Cell? (heard rumor that this could be their surprise game). Last splinter cell released 2013. But Ubisoft owns the IP, and would Ubisoft release a exclusive game for the Xbox  platform, avoiding potential of selling to 60+ million PS4 gamers?
• A new console friendly Age of Empires RTS? (could be big surprise. A beloved franchise for PC gamers)
• A new Perfect Dark Zero? (don't know the strength in that IP, but doubtfull it could be a showstopper)
• A new Fable? (yet Lionhead is closed, don't believe a new AAA Fable is underway)
• A new Gears? (That franchise has gotten tired, needs a reboot, but don't believe that is happening anytime soon)

They won't show halo 6 but they don't need to announce it we will see it next year.

They promised the Scorpio will do native 4k and deliver better quality experiences in third party games then the PS4/PS4 Pro so all they need to do is show this.

New games etc are not connected directly to the Scorpio but to the xbox platform in general, sure they need good games and crackdown 3 and state of decay 2 also need a good showing.

But most important is just the general thing that they need to keep their promise of 4k gaming and with the extra memory, memory bus and more powerfull hardware in general I think the scorpio will have a strong showing.

haven't they said last month that Halo 6 won't be at E3?

and Gears released last year

no, MS can't really recapture their audience/get new audiences with their established IPs at this point, they are in the undesireable situation to give the people something, that they don't even know they want

Halo and gears are tired. We need new games or return to ones that haven't been around in a long time. 

Splinter cell would be cool as long as its similar to Pandora tomorrow and chaos theory.

The one that makes everyone travel back in time and forget the disaster that was E3 2013 for MS.

If the Scorpio turns out to be significantly more powerful than PS4 Pro and has the best ports, that will be worth something.

MS needs to please their base, show more of the same content their userbase enjoys and announce some new big budget action games. A few fan service things helps as well, like bringing back classic IPs.

Without gears/fable/halo being there?
No idea. new IPs?

Halo 6: strong possibility, but only expect a teaser and the game to come 2018.

Splinter Cell: very unlikely as an exclusive for the reason you mentioned, although microsoft could grab the marketing lead.

Age of Empire: given the lacklustre sales of Halo Wars 2, this would be a big risk. 

Gears: Gears of War 4 was the reboot, the launch of a new trilogy and only came out last year. However you feel about the game, there won't be another major release until 2018 at the earliest.

Perfect Dark and Fable seem like dead IPs so Id be very surprised if there was anything major from them.

Xbox is very lacking in new console exclusive I.Ps. They need something new and fresh to attract a new audience.

only this