Cockos has updated REAPER to v5.96.
Changes:

• MIDI editor:
  • avoid hit testing against notes that begin before the active area of item and end exactly at the active are of item.
  • do not draw notes that begin before the active area of item and end exactly on the start of item.
  • handle notes that begin before start offset when duplicating notes octave down.
  • fix incorrect undo behavior when navigating notes via action and previews disabled.
  • fix issues with paste/duplicate notes and non-1.0 take rates, notes that start at negative project times.
  • fix multi-context selection undo with various actions and mouse behaviors.
  • fix undo for secondary contexts when using [un]select all actions.
  • optimize multi-context undo system.
  • preserve grid-enabled setting when switching contexts.
  • avoid inline editor flicker when resizing content and left edge.
• Notation:
  • allow editing both start/end of immediately adjacent items.
  • fix chasing of clef to start of media item.
  • fix create tuplet action when not launched via context menu.
  • fix marquee undo for multiple contexts.
  • improve multi-context selection undo behavior when unselecting via select phrase, pedal event, lyric, notation, tuplet, etc.
  • set armed cursor when using armed toolbar action.
  • fix various bugs in tick/QN to measure calculation.
  • update select all notes in staff action description to be more accurate.
• OSC:
  • fix FX parameter change notifications for last track in bank.
  • send FX parameter state for new plug-ins/loaded project.
  • send an integer value of -1 to fx/@/param in order to end touch state.
  • setting FX parameters always sets touch state, even if value did not change.
  • support receiving large (32KB) OSC bundles.
• Automation items:
  • fix possible project corruption when moving tracks to subproject.
  • improve selection tracking in undo state.
• FX:
  • paste after currently selected item in chain rather than at end of list.
  • improve behavior when dragging FX to its existing position.
• Linux:
  • fix scrollbar in routing/envelope windows.
  • fix slider precise-mode issue.
• MIDI:
  • fix glitches when editing the left edges of looped MIDI items.
  • fix negative start offset peak drawing issue around tempo changes.
  • fix peak drawing bug with non-1.0 takerate, looping, tempo changes.
• MusicXML:
  • support .mxl (zip-compressed MusicXML).
  • fix encoding-date month field.
• Preferences:
  • fix apply button behavior in project backup settings.
  • fix re-enabling of missing MIDI device warnings.
• Undo:
  • avoid repeatedly trying to reload track/item images after initial failure.
  • avoid unnecessary reload of track panel images.
  • fix loss of item background images.
• Video:
  • add spherical source mode to 360 panner preset.
  • allowing bypassing DirectShow video output on Windows (slow, but more compatible).
• VST3:
  • always apply any latent VST3 parameter changes before saving state.
  • fix popup menu position.
• Actions: add meta-action to toggle following action armed (rather than always arm).
• Command line: resolve relative pathnames passed on the command line.
• Item notes: copy notes/images to new item when using pencil-drawing of new items.
• Localization: fix elastique display on Cyrillic character sets.
• macOS: remove scrollbar drawing glitches.
• Performance: avoid loading multiple copies of track icon/media item background/info images.
• Recording: fix recorded offset of tracks armed during pre-roll.
• API:
  • fix InsertAutomationItem() undo bug, support creating AI pools with index, trim behind according to preference.
  • [Take|Track]FX_SetParamNormalized() always sets touch state, even if value did not change.
  • add GetAudioDeviceInfo().
  • fix [Take|Track]FX_EndParamEdit() when called immediately following parameter set.

 
Read more at  [link=http://www.reaper.fm]www.reaper.fm[/link]

Note that this version still has no ARA2 (Melodyne 4.2) integrated. It is planned for 5.97 and available in betas (f.e. 5.96rc3, where it works reasonably well).

I thought 6.0 was going to be ARA2 implementation... Totally burst my bubble on me.

Justin release things once they are ready for release, he does not bind himself to some version numbers nor dates
 
The reason it is no in 5.96 is the following: they have changed the way duplicated items are exposed to ARA in one of latest betas. That way was in rc3, when Melodyne 4.2 was released. The approach they have tried to use was not what Celemony has proposed, also some users (including myself) have found it more then confusing (I was sure that is a bug, till I have found the explanation...). So they will revert, but it was too late and too error prone to do this on in rc.
 
But I repeat, betas have ARA2 for LONG TIME! Without corresponding Melodyne only Celemony beta testers was able to work with that. But normal users can also test now.
 
People try to do crazy things with that... Unlike Sonar, REAPER does not lock the source. Melodyne can be just inserted as a track FX and ARA2 is used automatically. It is possible to put new clips/ delete / slip edit / etc. Obviously Melodyne has to re-analyze in such cases. And it does, but so far not always with success. I guess that is a great "stress test" for Celemony and can help spot and fix many bugs.
Sonar like "per item" FX also works, but there is no sound during tuning in Melodyne in this case (since in REAPER item can not produce sounds on its own without playback or item preview) and time position can not be moved till REAPER time position is within the item in question. I think that is just early implementation problems, will be fixed next days.
Other then mentioned inconvenience (also with "Ctrl+Z"...), it works fine. Also as multi-track (studio).