Well, I've (semi) successfully compiled PHP 6 on DH. I say semi because it kinda refused to work
Anyway, if anyone would like to try and compile it, it's pretty easy to do (I can say that after 6 hours of trial and error, heh). You should do essentially the same as with compiling your own PHP 5 for which instructions can be found on http://wiki.dreamhost.com/Installing_PHP5. You also need to make some adjustments to the installscript, namely update all the version informations to latest ones, (this shouldn't be done, but do it if compiler complains) change --enable-mbregex to --disable-mbregex and make any other modifications you see fit.
But before any of this, you have to first compile latest versions of flex, re2c and icu and then add the following lines to PHPFEATURES in installscript:
After the compiling I've set the handler to use PHP 6 cgi, but I got the 500. The problem wasn't in 0755, so it's probably somewhere in the compile process itself. If someone manages to make it work, please let me (and others) know here.