Larger changes represent more work on the part of the submitter ;) 
The following should reproduce the readline problem:

Have the current setup.py detect as the readline termcap library a
libncurses.so that itself links against libtinfo.so.  Without the --as-needed
flag, this is sufficient, since libtinfo ends up being indirectly linked to
readline.so, through libncurses.so.  Not that it was ever the right approach,
but absent --as-needed, it happens to work. 

Then, make sure the --as-needed flag is passed to the link command for the
readline.so module.  In that case, even though there is a "-lncurses" argument,
the linke will not link libncurses.so to readline.so because readline.so
doesn't directly need any symbols provided by libncurses.so.  The readline
module will then fail to load because terminal library symbols like UP will be
missing.

Without --as-needed, superfluous links between shared objects proliferate
through a software collection.  --as-needed is becoming more common, so it
would be good if setup.py didn't break because of it.