Back a little bit ago when the thread about running out of RFC-1918 space was going on, I was going to make a suggestion about repurposing the Class E space in the case where one ran out of space, assuming one could get the vendors on your network to support this address range.
I sort of discarded the suggestion just because of the whole issue of that range being hardcoded as invalid in so many implementations that this didn't seem all that useful.
On the other hand, if you're large enough that you're running out of RFC-1918 space you might be able to exert enough power over select vendors to get them to make this work for selected purposes. Router-to-Router links, especially between higher-end routers seems to be one of those cases that it might be useful. It might be the case that Amazon is already doing this....