Yep. Every few months, someone learns about this, thinks they've made a new discovery, and writes a breathless blog post imagining the possibilities of what can be done with it.
Spoiler alert, you almost certainly have been completely pwned already if someone can set LD_PRELOAD or modify /etc/ld.so.conf.
Please describe the scenario where someone needs to make the assumption you described and it is reasonable to expect that they are unaware that symbolic links could be changed by a third party library?
Maybe I misunderstood your argument, but /proc/[pid]/exe is a symlink in Linux 2.2 and later (so virtually all running instances of Linux today).
That said, your example doesn't make much sense to me. I'd be willing to bet a lot of money that the authors of the exploit chain you mentioned are aware of LD_PRELOAD and /etc/ld.so.conf.
I remember using LD_PRELOAD for reverse engineering Linux binary-only apps in the late 90's so it's likely from much earlier than that, always has been a neat trick
Spoiler alert, you almost certainly have been completely pwned already if someone can set LD_PRELOAD or modify /etc/ld.so.conf.