Concrete ties are on the to-do list for rtrax, though I'm sure issues will crop up with people trying to make switches with them instead of the wooden tie versions.
The only thing keeping me from doing non-oil stained versions of what exists already is that without some proper planning the track list can very quickly spiral out of control:
Right now there's three shades of gray, black, and salt & pepper ballast types, each of those types has three weights, each weight comes in welded and jointed, and each of those comes with polished rail heads or rusty... that's already 5x3x2x2=60 types in the dropdown window. Add clean ballast versions to each of those and suddenly there's 120 to pick from. Add a new tie type and that doubles again to 240 (!)