3.3 intention (as far as I can tell) was to 'get with the times'. Meaning to upgrade / update to all the latest dependencies. Such as PHP, Symfony (and Twig), jQuery, etc. Adding new features and functions, means that it will mostlikely cause issues with previous versions, and that was not the intention for 3.3, making sure almost everything from 3.2 is compatible with 3.3 - and even that is not true, as you've noticed by all the topics about the updated symfony versions. Some 'old' extensions that are mostlikely abandoned are still having compatibility issues with the deprecated syntax.
New (major) features are to be part of 4.0, which will mostlikely break BC, such as routes (
yourforum.com/user), browsing the CDB from your ACP, new style (Chameleon), etc.. It will move away from classes full of (random) functions and using
globals, to proper (symfony) objects. Where correct exceptions can be thrown and not a 'hacky'
trigger_error(). And services can be injected through a constructor (
__construct()) rather than passing them along as function parameters or through globals.
And about the 'live search', that feature was already there, I just did some enhancements to it. I made the 'loading indicator' visible and added keyboard navigation to the results, highlighting the selected username.