Sounds good. Here's a new patch set with aclitem's typalign fixed.
Patch applies. Passes make check and make check-world. Test coverage seems adequate.
Coding is very clear and very much in the style of the existing code. Any quibbles I have with the coding style are ones I have with the overall pg-style, and this isn't the forum for that.
I haven't done any benchmarking yet, but it seems that the main question will be the impact on ordinary DML statements.
I have no opinion about the design debate earlier in this thread, but I do think that this patch is ready and adds something concrete to the ongoing discussion.