Heres my 2c.
1. The beta page for p3dv4 is now gone (Suggests to me the beta is finished)
2. The finding of Website assets for the 05 month including p3dv4 logos and buy now banners, (The page is now locked access)
3. The Style of P3D website now the dark colouring which matches the leaked logo from Aerosoft's forum a while ago.
If I had to take a punt on the release it's by the end of May,