Hell yes! Absolutely I would buy a XXI boat. I would also like to see a IXB, a VIIA and VIIB. World War 1 U-boats also. And an American S-boat too. As for Japanese subs, people should ask for the I-19 in 1/72 scale. There would be plenty of interest in that one. I also would like to see them do an I-20, since Lindberg never released theirs.
What I have never been able to understand is why none of the Japanese companies have ever released a 1/72 boat, other than the Type A midget. Oh well, maybe someday..