Lots of Zelda & Starfox info
More third party collaborations
Retro's new project

Because I like my expectations low, that's why :)

I want a live event. They give us digital events year-round; make E3 special.

Then they just need to cover three games to make me happy.

The Legend of Zelda
Star Fox
Metroid (Hopefully a reboot to right the course of the series after Other M)

Agree with most of this except for New 3D Mario. I think at this point if they have a new game in the works, they might as well punt it to be a lead for a new console.

I will add:
Fatal Frame V worldwide this Halloween.
Devil's Third stuffs.
More Wii ports to Wii U eshop or n3DS ports. Some GameCube ports as well.

Sure things (100% chance of at least appearing in some form):

1. Zelda U, subtitle revealed, release date revealed in the holiday 2015 timeframe, trailer, possibly a playable demo

2. Star Fox U with finalized title, trailer, release date before Zelda, probably late fall

3. Xenoblade Chronicles X, final trailer, playable, release date before Star Fox, probably late summer to early fall

4. Yoshi's Wooly World, anything not revealed in Spring directs revealed now, playable, release date early to mid summer

5. Mario Maker, ditto to Yoshi

6. Project Guard and Project Giant Robot, more details, release date and playable if small titles

7. Fire Emblem: If, more details, possibly dated for early 2016 to spring 2016 in the west

Probable things (<100%, >66% chance of appearing):

1. Devil's Third, new trailer, new details, possibly a release window, unlikely but not impossibly a release date and demo

2. New mainline Pokemon, X2/Y2 or Z, first trailer, maybe some release details, maybe this year

3. Rodea, western release date, or at least a window

4. Some sort of New 3DS exclusive, hard to say what

5. Multiple uses of amiibo, possibly new figures or a new series (Zelda series, if Nintendo wants to shut up and take my rupees)

6. A spinoff of a major first party IP

Maybes (<66%, >33%, or hard to place otherwise)

1. Metroid 3DS, trailer, release window summer 2016

2. Metroid U, teaser, release window holiday 2016

3. Retro's latest project (maybe it's Metroid U?)

4. Fire Emblem x Shin Megami Tensei, either shown in some fashion this E3 or cancellation announcement by the end of the year

5. Animal Crossing U, depending on how far along it is (another good candidate for a new amiibo series)

6. Pokken Wii U, 2016 release

7. Project Treasure, if Bamco is ready to talk

8. Splatoon DLC, unless the game somehow isn't out yet in which case 100% chance of all details revealed and playable demo

Long Shots (<33%, >0%)

1. F-Zero, in some form, maybe even a new game

2. Earthbound/Mother IP finally utilized, probable just western VC localizations at best, though maybe some kind of localized collection

3. Paper Mario U announced (I see this happening next year if at all, though I do think it will happen then)

4. Fatal Frame localization

5. Bravely Second details (I see this waiting until later this year)

6. New 3D console Mario, of the "star hunting" variety

7. Long awaited 3DS localizations like Dragon Quest

That should be about 75% of the show, plus some indie and 3rd party reels. It'll be a digital event, with a smaller press release sort of event to use that theater they reserved for 299 people. That theater may be used to show off Zelda (crosses fingers).

Nintendo EAD Tokyo has two teams.  EAD Tokyo 1 and EAD Tokyo 2.  EAD Tokyo made the incredibly underrated DK Jungle Beat, then went on to develop Mario Galaxy.  EAD Tokyo 2 handled Galaxy 2, 3D World, Captain Toad, and Land.

Since developing Galaxy, EAD Tokyo 1 worked with Greezo on the remakes for Majora's Mask and Ocarina of time, although I doubt their input could have been that great since the game runs on essentially the same engine as the N64 game.  So, I dunno what they're up to.

Nintendo does have a conference stage booked for this year's E3, so they may do a small presentation at E3, alongside their digital E3 event.

As for already announced games, any that haven't been released by E3 will likely get updates. Major focus will be on Zelda and Starfox are the obvious ones confirmed already to have a presence there.
I think we will see a new mainline 3D Mario game announced, Metroid, F-Zero or Waverace announced with gameplay.
Some new IPs handled like Splatoon.

Perhaps Bayonetta 3 will be unveiled.

Probably some Starfox gameplay, Zelda U gameplay, more XCX, and more new IPs, but other than that, I've got nothing.

Super Mario 64 remake for Wii U.
Mario Kart 8 DLC Pack 3 and 4.
Smash Bros Wii U/3DS characters DLC
Star Fox U
Pokemon Amie game for Wii U.

-Starfox U trailer
-new rewards program to replace Club Nintendo
-Legend of Zelda U trailer
-Pokemon Z
-Pokemon Spinoff
-Pikmin something (remastred 1&2, Pikmin 4, 3DS game)
-New 3DS info covering the amiibo reader for old 3DS, and release date for public Flipnote 3D download
-new Metroid announcement
-more Wii games coming to Wii U
-a ton of eShop releases
-news on DS, GC, and N64 virtual console
-Animal Crossing U
-Project Treasure
-final Splatoon coverage
-Mario Maker
-new Mario announcement (SMG3)