My guess is it would be related to the upcoming smith skills. From what I gather, any weapon you use, you can earn smithing skills with which will allow you to smith those items in the upcoming strategus with the right materials. Therefore, if you could transfer heirloomed items to your main from your alt, you could also gain smithing skills with them and craft them.
Though personally, I don't see how the effort you put into an alt should be ignored and valued far less than the effort you put into a main. It's not like an alt is any easier to retire with.