This is a meta-issue of the issues needed to bring WSCCI through the home stretch and cross the D8 finish line!
REST clean-up
#1970360: Entities should define URI templates and standard links
Router
#1505080: [META] Content Negotiation for Accept HeadersAssigned to: scor
#1889790: [Meta] Allow modules to register links for menus, breadcrumbs and tabs (if not with hook_menu)
#1908756: Separate Action Links (MENU_LOCAL_ACTION) from hook_menu()
#1954892: Figure out how to deal with 'theme callback'
#1947536: Convert drupal_get_breadcrumb() and drupal_set_breadcrumb() to a serviceAssigned to: donquixote
Clean-up
#1888424: Make Drupal's URL generation logic available to HttpKernel, and minimize code repetition/divergence
#1858196: Add Implementation of Symfony Session to DI Container
#1858198: Implement Symfony's Session handling in core
#1858200: Implement secure session with Symfony's Session object
#1938980: Move controller derivation to route enhancers
#1941288: ajaxPageState not being updated with AjaxResponse, assets (js/css) being added twice
Page Cache
#1830854: [meta] The ESI pipeline battle plan
#1597696: Switch page caching to HttpCache
#1945024: Switch from FrameworkBundle's HttpKernel to rendering strategiesAssigned to: Crell
Conversions
#1971384: [META] Convert page callbacks to controllers
#1668866: Replace drupal_goto() with RedirectResponse
#1623114: Remove drupal_exit() and other exit calls
#1911178: Remove hook_exit()Assigned to: catch
#1911728: Remove hook_init() in favor of kernel.requestAssigned to: Xano