I think he means bringing the Virtual Instruments from ReBirth into Reason. Not a bad idea at all.
And yes -- Dr. Rex needs to have as many of recycle's tools and capability crammed into it as possible. No reason you shouldn't be able to create your own Rex from within the Reason Environment. Having to have a separate program (but you can otherwise record audio into Reason/Record) makes no sense at all. Nearly all of the other programs will allow loop slicing and processing of a raw audio file from within.