getlastmodified and ISO8601

At the last IETF in Was DC, it was suggested (by me I think) that we should
change the <d:getlastmodified> property from using HTTP-Date to ISO-8601
dates.   I would like to do this now before to many clients and servers
exist, and we can never change it.

Many people at the meeting agreed with me, but we did not know what problems
this might cause existing clients and servers.

So here is the question, can we make this change.

Xythos currently uses HTTP-Date, but we will have no problem updating to
ISO-8601 (and then patching our client's servers).

Thanks,
Kevin