Just like 5.0, 5.1 consists of a “Dual-kernel”. On the left side you’ll see the legacy stack, a an enhanced and stabilized version of the 4.x kernel. On the right side is the 5.x stack, with the arrows indicating some highlighted improvements made since 5.0.
Persistence DB cache using Stash
Twig Helper (ezpublish & ezpublish.legacy global variable) [PR, Doc]
Symfony Locale integration [PR, Doc]
Multisite with single content repository [PR, Doc]
GraphicsMagick support [PR, Doc]
Add option to allow Twig template to override rendering of legacy requests [PR1]
REST support for session authentication with CSRF token support [PR1, PR2, Specifications, Doc]
Thousand small and + hundreds small/medium improvements & bug fixes in Public API, REST API, legacy and Demo bundle, see full change-log below.
With 5.1 out the door, our focus will shift more towards new 5.x based user interfaces while also improving the 5.x stack further, in no particular order:
HTTP cache for logged in users, Profile detailed performance tracking, use Symfony 2.3 Proxy services, further profile & improve new kernel to speed up uncached execution
Symfony based login, full Bundle based permission integration
for easier re-use in custom Bundles, ..
Future improved database handler and File storage to cross the 1 million content object soft barrier
New stack configuration, improved database and file storage that can scale across many servers and datacenters, Async event handling with background daemon
Solr support, REST Oauth support (Symfony Bundle), WorkFlow, Subscription/Notification, Import/Export, REST Oauth support, Solr support w/ ezfind integration
|5.2/5.3/*AdminBundle, EditorialBundle, front||future|
Front end editing, UGC, language switcher, AdminBundle, EditorialBundle & Setup UIfunctionality
Tags, Page (ezflow) write support, Matrix, Identifier, XmlText html5 (editing and REST) & easier XMLText custom tags, Improved Media/Binary field types for cloud storage/CDN needs
|Extensibility||Criterion, SignalSlots, REST server, Limitations, code generation, ..||5.2/5.future|
Content (Search, ..), webshopComments (using content model), InfoCollector (using Symfony Forms), RSS, Staging, tip a friend, Rating
For much more fine grained and additional technical info , see on feature naming and comparison between 5.x and 4.x, see this community maintained Google spreadsheet.