Conclusion: we will not see much change in the single target playstyle. But the aoe playstyle change will be very drastic and leads to 2 different aoe builds.
Basics:
The existence of the vampiric insight trait as well as the last 3 rows of the talent tree means dotting as much target with vp as possible will become rewarding. To be specific, some traits directly says more vp leads to more procs and more dmg(nzoth line). Some others empower shadowy apparition, which only procs on targets dotted vp, as well as vp increases the number of mind blast we can get in the form of vampiric insight trait. The rest of the traits is tied to mind sear and monomania trait, which only works on targets with vp dotted.
Because vp is elevated to such a crucial position, extending its duration on multiple targets will be extremely rewarding in multi target situations. There are 2 primary ways to do it: casting void bolts, and casting mind sear(supported by the rot and wither trait).
Potential combinations:
void bolt build: void form and hungering void greatly increases the number of void bolts we can cast so those traits are a must take. Because void bolts procs shadowy apparitions it is natural to pick the path emphasizing more on shadowy apparitions than the monomania-mind sear path. Not to mention to utilize monomania trait we want to cast mind sear as much as possible, which conflicts with casting void bolt.
Take psychic link and shadow crash vs void touched and void torrent depending on aoe vs single target situation.
For the last talent points it is void echo + vp and dp dmg vs talbadar and better dark thought procs. These traits are all heavily tuning dependant, but the generally playstyle is to spread vp before casting void form, stay in void form to refresh vp on targets as much as possible. Since voidform is obviously an offensive cooldown this build will be bursty, and will benefit greatly from critical strike and haste to not only increase voidform duration, but also generating more shadowy apparitions, more dots procs, and more mind blasts.
Also imagine if living shadow procs not only mind blast, but echoeing void, shadowy apparition, void bolt, and gives us an additional vp.
In case living shadow becomes divine image, remove points from fortress of mind. Take void touched, torrent, mind link, and shadow crash. Opt into talbadar, eidolic and yogg saron. This build sacrifice some amount of shadowy apparition dmg to pick up less synergizing mind sear traits, while the yogg saron and eidolic traits still synergize with the rest of the build.
Mind sear build will be updated later.