Has anyone heard anything about a manufacturer that may be working on a scanner that will be able to monitor Mototrbo systems?
No. You can count Uniden out at this point since they just announced their newest series and it doesn't include MotoTRBO as one of the modes it works on. That said, they may be working on it, but if so it will be quite a while for them to introduce it (they appear to have a two to three year cycle for new models).
There's still hope for Whistler (the group that's taking over the GRE line of scanners), but since they're just starting up it'll be a while for them as well. I wouldn't expect any brand new models from them (only Whistler branded versions of what GRE was making and selling) for at least most of this year.