I just finished discussing how Grand Theft Auto IV's mod community thrives almost in spite of not having an official toolkit. Apparently, at PAX 2014, Volition announced that Saint's Row IV's official development kit will be released to the public. This follows their announcements of Saint's Row 4: Re-elected, an updated version for PS4 and Xbox One, and Saints Row: Gat Out of Hell, a spin-off of Saint's Row IV for the PS3, Xbox 360, PS4, Xbox One, and Windows PC, that claims to place the Third Street Saints in a Disney-esque musical set in Hell.
As usual, I encourage as many developers as possible to release their development tools to the community. If you have a good game, and the community believes they could make it even better, that could help you. This seems obvious but has some development costs and (irrational?) fear of eating into DLC sales. On the other hand, it could help promote your product and its DLC, spin-offs, and so forth… see above.