The ebuilds for scilab-3.0 and scilab-3.0-r1 have the "~x86" and "~ppc" keywords set. Is scilab 3.0+ not yet ready for primetime? Also, there is a scilab-3.1 release canidate and should be out soon.
Version 3.1 is in CVS now. I don't think any version of Scilab will be marked stable in the near future, since there are problems with "virtual/blas".
FYI, I get the following error when trying to emerge SciLab-3.1.1: !!! Security Violation: A file exists that is not in the manifest. Think this one needs to be sorted...
My bad, probably. I must have broken something when commiting some changes to Scilab. It should be fixed now. (Next time, please open a new bug report if your issue is not the same as in the original bug report.)