dev-tex/dvipost depends on virtual/tetex, which does not exist. Emerging dvipost will pull in app-text/tetex. I think dev-tex/dvipost should depends on virtual/tex-base. Reproducible: Always
In fact this problem happens during emerge app-office/lyx, which depends on dev-tex/dvipost. The new profile now take texlive as the default tex-base system, but here emerging lyx pulls in dvipost, thus tetex again, which is blocked by texlive.
virtual/tetex does exist and texlive includes the necessary provide clause (for now at least), so there is no such problem. Please provide more information.