About the custom prebuilds I see that it enables support for more recent versions of nw.js (I'm currently using Greenworks + Nw.js 0.33.3), but could you explain the benefits to use more recent versions of nw.js ? I haven't seen this anywhere... I'm not really familiar with Node webkit updates and so far on this particular subject my position has been : "if it's not broken, don't fix it", but if I'm missing on something I might upgrade my game! ^^
Software updates always contain important fixes and performance improvements. NWjs specifically got a complete overhaul of the window tech, which fixes a lot of issues with Steam and certain types of game recorders. I never tell people to use new or specific versions of NWjs because there can always be unexpected issues and downgrading can sometimes be problematic.
I also felt quite restricted by the current official Greenworks ACEs so I'm considering updating to Greengrinds to support future DLCs for example.
That's pretty much up to Scirra. There are TONS of features that could be supported but I guess there aren't enough Construct Desktop/Steam developers to justify Scirra to put the work into it. I don't know how Scirra prioritizes things so your best bet is to ask them directly, that's just my opinion.