At last count, I understood that jump tables do nothing to solve the
library data problem.  Has that been solved?   If so, just adding
jump table support to GCC, won't solve the problem.  Sorry to burst
your bubble, but as one who worked on implementing shared libs for
linux, and one of the first to admit it has warts, every wart has
a positive side.

First, jump tables have a performance hit.   And using them may
never work, since the change of one interface will screw the upgrade.
Worse, if an interface changes without us realizing it, then our 
programs could just start acting strange (far worse than broken).

The current implementation of shared libs has two main characteristics:
simple and reliable.

Of course, I would love to be told I am wrong :-)