Looking at the comments on reddit, I figured that I would say that luatex does resolve pdfTeX's internal limitation of 256 glyphs that I mentioned in part two, and it should directly support OpenType fonts with PostScript outlines.
However, my understanding is that the authors of luatex do not intend to make using TrueType and OpenType fonts as simple as XeTeX directly. Instead, luatex merely makes the machinery available for someone else to build upon. So someone will need to write a LaTeX package for luatex to put it all together, and as far as I know, no one has done this yet (let me know if I'm wrong!). Also, while the plan is for luatex to eventually be merged back into pdfTeX, I think it is an overstatement to say that it will happen "soon". The current luatex roadmap says that a "production" ready version will be available in August 2009. I doubt that the merge back to pdfTeX will happen any sooner than 2010 given that. But yes, in the long term I think luatex will be a great thing.
It also sounds like I should probably write a fourth part to my tutorial on using fontinst. I've never personally used it myself, and when I first started working with OpenType fonts and LaTeX I wasn't aware of its existence. Therefore, I wrote otftofd. So it might take a bit longer to write as I will have to learn it at the same time.