We won't be doubling up the content of Half-Elves and Humans. Half-Elves can choose to use either the Humans book or the Elves book-- or, if your GM is generous, both. We mention their options briefly in the impending Elves book and will do so again when we get to humans.
As I mentioned in the ENworld interview we did a while back, our plan currently is to cover Humans in a hardback anthology (titled, simply, HEROES OF HIGH FAVOR). It will combine content from the other books as well as remaining multiclass combos, plus new stuff for each race that we couldn't fit into the smaller format, plus a ton of new general "human" feats, new skills, etc. I am really looking forward to working on the layout on this one, as it will be a full-sized book (not 6x9) and no pretermined length, so there is some room to really stretch my creativity!
I will see about those T-shirts again... I apologize, they haven't been a top priority, but I feel silly passing up free the advertising you're offering!Wulf