Waiting anxiously for this Knight!Looks like it worked. I removed /preinstall and gave it all to /data, and recompiled a new kernel with all mention of /preinstall removed from it. Booted up, and it shows 3.2GB for data when I look in Applications.
The only weird thing was, when I removed /preinstall, I figured it would renumber /cache as mmcblk0p1, but it didn't... it stayed mmcblk0p2.... which is a good surprise, cause now I don't have to adjust the mount points for /cache anywhere else.
I am going to test the phone a bit today before I release the kernel I made and the instructions for completely removing /preinstall.