This isn't directed at you, but that sounds like exactly what I'd expect of someone who doesn't understand the point of package managers.
2. I'm pretty sure path prefixes can be used and the same set of pkg management tools can be used to install in user land. I've done it in the past into an env I was chrooting and minifying to power a picture frame.
As paths to libs and stuff are hardcoded as part of the ELF spec, it becomes difficult to implement something like this and ive not seen a package manager that can do it.
It would be interesting to think more about user-level applications and how that sort of trust would work, if it could.