Are there plans in the near future to introduce Fedora Core compiled for 686 processors?
(Almost) all rpms in FC are built with -march=i386 -mpcu=i686, meaning that they are optimised for 686 but will run on all 386 hardware. Certain key packages, such as glibc and kernel, are built for specific architectures, i.e. -march=athlon or -march=i686. That's being done in the areas where the largest benefits are made.
In general, I'd say no one has been able to prove that compiling each and every application with aggressive optimisation and/or architecture specific instructions give any measurable speed improvements. There are several compiler experts on this list that can explain why.
That said, if anyone can point to a package that would benefit a lot
(more than 5%) from -march, I'm all for including that in FC. But show the numbers, no "man, -O3 made KDE so much 'snappier'!" stories :-)
/Peter