I have always thought the aftermarket should address the idea of a lower high range gearing for Toyotas in some form, so I'd love to see somebody try this.
I am sure you know that the factory high range is a straight through design where the input and output shafts are simply coupled in high range to achieve the 1:1 ratio. In order to achieve a higher high range ratio in an rf1a transfer box one of the housing sections would have to be completely re-cast. I suppose it could be done similarly to how the additional low range box is done, by simply adding an intermediate gear housing. Maybe you should start work on the prototype H8PVMNT?