My comfort level would be much higher if by the time that we need the extra address space, we have a fighting chance of actually being able to use it. So I think it would be a good idea to make it very clear that implementations must, in the absence of more specific information, regard class E space as regular unicast space, the same way the IPv6 addressing RFCs spell this out for IPv6 address space that hasn't received a specific purpose yet. If we do this now we have ten years or more to clean up implementations.
The only way to make this happen would be to start assigning them to some real users. Otherwise, the bugs will not be found, reported, and fixed. Just publishing an RFC with a MUST in it won't be sufficient.
The challenge here is that there may be a lot of IPv4 implementations may have little or any support, and may not be possible to upgrade. This would put anyone receiving a Class-E address at a big disadvantage. These addresses might have to be used behind a NAT to be useful (i.e., allow direct communication to the rest of the Internet) and this, of course, defeats the purpose of using them in the first place.
Bob
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