Here's my list of things I'd be overjoyed to see fixed / announced / released at WWDC 2015 next week.

iOS

• Deep linking support. Let apps define associated URLs (https://twitter.com/* –> open Twitter.app).
• Really want to hide my carrier and clean up that status bar. Such a mess right now.
• It's time to modernize the UI for Notes.app and Reminders.app. iOS 6 was years ago.
• Save alarm and world clock data in iCloud. Re-adding this on every device is really tedious.
• Export Health.app data or save it in iCloud with a password. At the moment, it's not shared between devices and will be lost permanently if you don't have an encrypted local iTunes backup of your device.
• Needs to be a way to close all tabs in Safari without tapping the screen 50x times. Absurd.

Mail.app

• Search that actually works. Right now this is the only reason I still have the Gmail app still on my phone. I open it up whenever I want to search for a message.
• Send from an alias like Gmail web client lets you.
• Better UX for labeling threads.

Maps

• (I've mentioned this on Twitter) Fix the UX with reviews of physical locations.
• Public transit support.
• Improved traffic data.

App Store

• Search. Need I say more?
• Direct refunds without iTunes support involvement.
• Responding to reviews would be nice.
• Expire old reviews (1yr+) when new versions of app have since been released.

Safari (OS X)

• Reopen more than the most recent closed tab in Safari.
• Paste images into web pages.

Xcode

• Stop beachballing so darn much.
• It would be nice to stop an archive action without needing to restart the app.
• Debugging extensions is currently a huge pain. It would be nice if it were easier.

Added 6/7/2015

Photos on OS X

• "Show in Finder"