The difficulty in defining "kind" arises, in part, on the multiple different things that cdesign proponentists need the word to do.
First, and perhaps most important, is that humans are a different kind from everything else. I truly suspect that most cdesign proponentists would be content to accept everything in biology if we could separate humans from the rest of life. Humans are a "special creation," and that's the crux of a cdesign proponentist's objection to biology.
The second, and next most important, thing that cdesign proponentists use "kind" for is to try to save the flud myth. They've ultimately come to grips with the fact that the flud story is more difficult to believe than Santa Claus if the ark had to include every species on the planet. So, they invoke "kind" and argue that only a very small percentage of all current species were on the ark, but there were massive, extraordinarily rapid evolutionary changes afterwards to get where we are today.
Obviously, for the word "kind" to do either of these things, precision of meaning is not only unnecessary but can actually be a detriment. If "kind" is too broad, it will result in humans being biologically related to other primates; too narrow and the flud story becomes (more) ludicrous. The fact that there is no middle ground where the term can do both jobs at the same time probably has not escaped the more educated among cdesign proponentists. This is why it is so difficult to pin them down to one definition, there simply isn't one that will do everything they want it to.
There are a few other needs as well. We saw Calypsis insist that the bats are included in the "kind" referred to as "fowls," with other things that we now know to be birds. "Kind" is also used to describe the way all of life was created. Genesis describes the creation events in terms of the different "kinds."
The bottom line is that "kind" means whatever a cdesign proponentist needs it to mean at a particular moment. And by necessity, it can never be any more specific than that.
Please bear in mind that I wrote this rather off the cuff and at least two beers into my Vikings pregame ritual, so one or two of the details might be a bit dodgy, but the overall analysis is sound.
Ridicule is the only weapon which can be used against unintelligible propositions. Ideas must be distinct before reason can act upon them; and no man ever had a distinct idea of the trinity. It is the mere Abracadabra of the mountebanks calling themselves the priests of Jesus. -- Thomas Jefferson
For we know that our patchwork heritage is a strength, not a weakness. We are a nation of Christians and Muslims, Jews and Hindus -- and non-believers. -- Barack Obama
We see monsters where science shows us windmills. -- Phat