It would give more transport overhead, of course, and as MIP is already basically a traffic tunnelling proposition, it makes not a lot of sense to me personally ,:-) But yes, this could be done - now we have to wonder if it is sensible enough that we should increase our matrices with another dimension and include this in the draft :-)
I'm not sure if the matrix needs to be expanded; I took this to be just another solution approach to the case:
2 IPv6 MIPv4 IPv4 IPv4 "IPv6 in MIPv4"
Yes, with you so far, but if there are 5 possible reasonable tunnel solutions, in addition to adapting MIP4 to carry IPv6, should we discuss all of those? And accordingly for IPv4 in MIP6 ?
-- Pekka Savola "You each name yourselves king, yet the Netcore Oy kingdom bleeds." Systems. Networks. Security. -- George R.R. Martin: A Clash of Kings