The two biggest issues are 1) it's trivial to bypass:
$ /lib/ld.so /untrusted/path/to/program
and 2) that there's no (visible/vocal) user base calling for the feature.
About the point 1), yesterday i wrote just a simple regression test
(that can be found at the same place as the patch) and of course it
bypasses, this is an old commented problem, Stephen suggested the use of
the mmap and mprotect hooks, so, i will have a look at them but i'm not
sure on how to (really) prevent the dirty,old trick.
About 2), just give it a chance, maybe it's useful and my work is not
completely nonsense.