BobF
I've always been suspicious that Cake either lost the P5 code, or didn't own it outright to begin with.
 
Who knows, maybe Bitwig bought the P5 IP and created Bitwig with it.

i got impression that the lead dev for that left, and the lead-in time for someone else to pick it up was too costly. also, the codebase might have needed quite some work to make it (a) x64 native, and (b) multi-core aware - they were the two things i seem to remember us all wanting when that bad news hit... anyway, i moved to live back then, couldn't be happier

I have Live 10 now, but whenever I open P5, I still ask 'why did they ever let that one go'?

From what I remember there was one baker who worked for a year to add audio to P5.  And Rene programmed Dimension for it, Cakes first great synth (in my opinion).  P5 V2 was was a package deal and a step up from the Reason-like midi softsynth and player that was P5.  And at that point Cake had two nice DAWs - one for more traditional musicians and the other "electronic," more loop-based musicians.
 
From what I remember from Noel (excuse me if I have this wrong), he didn't see if any sense in developing P5 further.  It would be easier to clone on P5 aspects to SONAR than start piling on code to P5 to get up to SONAR standards.  Tho I know nothing about programming, I had assumed it would be less problematic to add to the "clean" structure of P5 than poke a stick at the old code in SONAR.  One thing I'm sure of, tho, now, is Cake was right not to mess w/ SONAR - look at the response to going from 8.5 to SONAR.  A lot of the old users freaked out.  Imagine trying to get them to buy P5 V3.  And everyone who loved P5 might have balked at having a bunch of extra crammed onto their screen.