I don't believe he is digging his heels in.
Yes his first 2 replys may have seemed a little heated / defensive (which is somewhat a no no for a dev.....no hard feelings paul), however he has posted in the CC post and over the forums that its just an idea.....
Probably one of many that have been floating around the office over there, many of which are probably taken from the forums believe it or not, or at least influenced a little by them.
Him only saying that particular one may not have been the wisest choice, but he did add after that it is just an idea and they will probably test it out just to see what happens......along with all the other ways they would like to check out.... (not on the live server of course, but internal. The eventual PTR will hopefully also see these types of ideas tested I'd say)
So he is right, in that you shouldn't jump to the conclusion that the idea he posted is the one they have chosen, and that its exactly designed like that & set in stone. You should most definitely still give feedback about what you think of it....which has happened, just don't treat it like its the only idea or coming instantly next patch when they have said otherwise.