It is always the edge cases that will kill you. In the case of WP on PostgreSQL, the reason you want WP in the first place is the plugins and those will be hit or miss on PostgreSQL. Just give up on the combination of those two.
To clarify, the wire protocol is the easy part, the semantic differences how each database does things is a whole other can of worms. Such emulation will never be 100%, quirks and all.
