I agree.The point about rats is that they are of genrralistt design, so suitable as a base for adaptive radiation.
I just expanded my response to address lurkers that I don't pay any direct attention to and that desperately need the increased understanding that comes with a fuller, less biased representation of the facts. However recalcitrant in denial they might be, I think any lifeline to help them out of their box is a noble, if none-the-less wasted, effort that is mine to waste.
Considering that small mammalian ancestors similar to modern rodents previously succeeded in forming the basis for the present adaptive radiation under similar conditions, I think that modern rat species could do so again given the conditions you put forth.