I think his main hesitation is threefold...cost number 1, a module like this will likely be 90-110USD. Number 2 if he spends the time and money to develop the module he needs to sell a fair number of them to recoup those costs which is totally understandable and number 3...he's worried about number 1 and 2 making the offering a losing prospect although initially there will be a number of us that will buy the module. Is that enough ? The other possible line of thinking is how much would such a DAC cut into sales of the DAC19 ? That may seem silly but IMO the FUN already competes well with the older C-2C (amp wise) so it's not a crazy thought by any means to think the DAC section thus equipped with a 2 chip pcm170UK module might give one 75% of the DAC19's resolution. IMO that's a positive for the FUN as it would clearly destroy any combo unit made today (if it hasn't claimed that spot in the under 600USD category already).
Anyway I still hope Kingwa decides to make an effort. He could adopt a group buy methodology for such a module thus guaranteeing a certain amount of money coming his way for his effort. Say lots of 10 units at a time. No discount of course.
Just throwing some thoughts and a suggestion or two out there.