the installation of readline-7.0 causes the rm of /lib64/libreadline.so.6 which in turn instantly breaks bash, lvm2, and run time dependences of portage and paludis. This results is an unusable and unbootable system. After booting from cd I was able to manually restore libreadline.so.6.3 and libreadline.so.6 to /lib64 which allowed a reboot so I could rebuild the 45 packages broken by readline-7.0 I don't know how portage handled the upgrade but paludis broke things big time.
commit 61452c1e8cfb3f31ce22b1c1111290268c36846b Author: Lars Wendler <polynomial-c@gentoo.org> Date: Wed Sep 28 07:41:01 2016 sys-libs/readline: Re-added preserve_old_lib for bug #595324. Package-Manager: portage-2.3.1 Signed-off-by: Lars Wendler <polynomial-c@gentoo.org> Sorry for the inconvenience.