It has been eight months since I posted this.
I would like to add more if you guys don't mind

Let's get started.
1- Keywords:We do not need keywords meta tag any more. So please remove it. None of the modern search engine uses it. (I don't know if any other search engine still uses keyword tags)
2- Personalise the control panelI always thought it would be really good to add your own short cuts and buttons and change the menu items under backend.
3- 2 step authentication: Google Authenticator, SMS or hardware authentication
I know there is an extension (admintools pro) and I am using it. I love it...(Also I have heard great things about YubiKey.)
But it does not support the frontend login. So in other words, if someone knows the super admin passwords, they can edit your website unless you forbid the frontend login using the super admin account.
4- Reactive DesignImages: Will they get smaller on a small screen? (Not html resize but small in size and the dimension) or ability to exclude images if people are seeing your site via mobile device? Ability to provide different formats for each device: Retina ready display formats as well as for normal lcd displays, mobile displays etc.
Site Design: Ability to let your visitors decide what modules they want to see and their position. What kind of colours they want? Personalised experience under their user accounts or without their accounts using cookies. (Every user of your website will have a personalised setting to receive/see a particular content) Maybe font increaser for people who have disabilities. Asking their feedback on annoying commercial advertisements on your website for example. Joomla automates the process and knows the users when they visit your site?
Responsive Design:Tables: When you create a html table within Joomla! website article, will they also be responsive?
Mobiles: Will they see all your website and keep on scrolling to be able to reach the bottom? or will you be able to SELECT the important content for mobile users? (Featured content for mobiles and tablets only?)
5-Ghost JoomlaI think this would be the most important security feature for Joomla! 3.5.
You know it is Joomla! website when:
you see com_ and mod_ everywhere inside the source code.
Maybe ability to customise those without manually going through particular component or a module or a plugin?
I think this will dramatically make the Joomla! sites more secure because people will not be able to search for particular plugins or components or modules on the internet and find out that they are vulnerable.
That's it for now.
I love Joomla! and can't wait to use the version 3.5
