I've never read anything concerning the removal of neg planes in AD. In fact from what I've seen in AD17 they've added some features for managing planes.
I do a lot of designs with Altium - been an owner since 1995. I do about 130 design a year.
Currently working on a design that has 12 layers with 10 being planes with splits. There's over 82 split planes. If I were to do that with internal polys it'd be a nightmare.
In fact, AD17 has some issues with nested split planes causing hangs in being able to save. Check the Altium forum posts.
As to top/bot pours again I stay away from that. A lot of designers love to add outer layer pours with the idea that it'll somehow aid in EMI emissions and susceptibility. In fact, at the local test lab, we've found it can actually exacerbate radiation due to things like return paths, coupling, etc..
We did a design for a medical device for a leading medical device supplier where one of the engineers wanted us to do outer layer pours. So we did (even stitched it with vias) and the result was just hideous - "... congratulations, that's the highest EMI we've ever seen in the lab" was the comment from testers. When we removed the outer layer copper it passed.
It also creates uncontrolled coplanar wave guides, that for most designs are not an issue but as you get into higher speed signals can have a detrimental effect on impedance. Also on multilayer designs you now have to deal with asymmetric striplines.
There are good reasons to do pours ( as in CPW) and the like, but you really need to know what the topology requires and design to that. Even high-end field solvers/post layout simulators can fail to find issues that can be caused by randomly pouring copper.