Just for an overview, here my assesment over the features we planned to have in the release and what we actually have now.

Originally, the main features of 4.0 were planned to be Zapper's new controls and content creation for settlement scenarios: challenges and means to overcome those, improving the scenarios and objects we already have, add flora, fauna and athmosphere.
Minor and personal projects were JCaesar's floating point, Clonk-Karl's rope system and PeterW's dynamic lighting system.

Planned features that were not done

Zapper's new controls: Turned out to be also an overhaul for the HUD which in future shall be based on customizable engine-side GUI. Bigger project than expected. Work on it stalled for 8 months now. Not expected to be continued/finished anytime soon but progressed too far for being abandoned I think.

JCaesar's floating point: Other than announced, no work done on it for 1 year. Probably abandoned.

Clonk-Karl's rope system: No work done on it for 1 year. Probably abandoned.

PeterW's dynamic lighting: No work done on it for over 1 year. Sadly sadly, I don't really see it being finished anymore since this project has been going about since 2009. Even though I would really like to convince myself to no see it dead.

Features that were later understood to be part of the next release but no work done

Carry heavy materials: Clonkonaut wanted to revive this and merge it into master but no work done. Since this is not that big of a task, I don't see it lost but probably not put into a release that we want to push right now.

Graphics overhaul / add missing 3d models: Fungiform's and Nachtfalter's project started out quite exciting but after an initial boost it left us with no results. I don't see any results coming anytime soon I am afraid.

Add architecture Mac (again), this time included into autobuilds: Very sad that this team effort (mac buildserver - Mortimer, autobuild scripts - Isilkor, web download frontend - Newton,  development versions - Clonk-Karl) was not carried to the end. It seems that from the sides of Mortimer, myself and Clonk-Karl, everything is ready to set up, Isilkor didn't finish his part.

The league: Not finished yet. There seems to be more to it. I hope we can start a beta after the new release.

Features that were (instead) implemented

+ added firestone material (Newton), pickaxe can't mine through everything (Sven2)
+ reworked solidmasks (Sven2)
+ introduced a completely new, more powerful and faster particle system (Zapper)
+ many documentation updates (mainly Newton)
+ introduced new way to create dynamic landscapes, Map.c (Sven2)
+ introduced cleaner way to create scenarios, Objects.c (Sven2)
+ add cave mushrooms (Zapper)
+ add many sound effects (mostly Clonkonaut)
+ debugrec option, intead of #ifdef - easier debugging for network bugs (Mortimer)
+ make keyboard input independent of keyboard layout (Newton, Oliver Schneider)
+ reduce install size by 10MB or so (Newton)
+ pumps can create power (Sven2, Newton)
+ added mape to main (Clonk-Karl)
+ new settlement scenarios (I don't have an overview over that)
+ lots of minor improvements to existing scenarios and objects (mainly Maikel, Ringwaul, Clonkonaut)
+ !!!quadrillions of bugfixes!!!, more than for any other version of OC and even much more than visible in the bugtracker (mainly Newton, Sven2, Isilkor, Maikel, Clonk-Karl, Mortimer)
+ forgot something?