Maybe they will surprise us with the Feb 5th event and announce Linux support starting with The Witcher 2.
I am afraid pigs will be flying in a frozen hell before that happens.
I see nothing wrong with an installer that just asks for a single directory to install in and optionally creates links to /usr/local/bin (if permissions permit). This is how it's been done a lot since Loki ports. It works, it will never hose your system as long as you don't run it as root, and when you need to uninstall you just delete the whole directory.
Package management is a great tool for some things, but in here I can only see it getting in the way.
For OS X, many developers/distributors, including GOG, don't even use an installer, but lets the user copy the package wherever they wish since it's quite self-contained in a form that doesn't really exist on other platforms - a folder that is treated as a single file and launches the application rather than opening in the file manager.
Package managers are a bit differently, they install applications for all users (/bin and /usr/bin) which is especially useful for getting updates.
So the only problem you might have by putting stuff in your home dir: you won't get automatic updates which is pointless here anyways.
If it's about your own system: why would you do that there?
So you're talking about preventing your kids from breaking stuff. How is that related to noexec? Without root access there's no way to break anything, except their own accounts and mounting a partition noexec won't even prevent that.
Granted, there are situations where you might gain root access via exploits but if your kernel is not patched and vulnerable to something like that you're in trouble anyways.
Those systems were indeed designed the way they were and that was: a multiuser environment were applications are executed with user privileges. Also, keep in mind that ANYBODY with physical access can compromise your machine at will. It doesn't matter if you're using Windows or Linux. You could simply boot from a rescue CD and chroot into your installation.