Regarding the core erosion issue, after my p4 died after 4 months of direct die (exact cause unkown since other extreme mobo mods we're in place as well)
link it had...marks on the core that corosponded to the impact points of the jet's, but they we're so faint that a wipe over the core removed them, mabie a deposit build up of some kind.
I have plans in place for a T-bred direct die exprimental block (quite similar to your approach actually) that also will try and address the porus core sealant issue.