And since it is a whole new, independent program, in the near future you will not need the original MSTS any more, at all, provided that freeware authors include the default MSTS textures in their route and stock packages !
Theoretically those things are still copyrighted by Microsoft, but since the MSTS is a ten year-old program and they are not selling it anymore (except in cheap licenced copies by third-party companies) I doubt there would be any problems in reality. Microsoft is not going to enforce its copyright on a couple of old MSTS shapes and stuff, as long as you do not distribute the whole MSTS program complete with the exe-files on the web.
And for those who want to be 100% on the safe side there is no need any more to use any of the default MSTS shapes and stuff, since there is so much more freeware replacements out there !
Ultimately, OR will get its own route editor and other tools, too ! Though those are not included in the coming release, this is still gonna take a while.