I've been spending time lately learning more about working with METATYPE1, mostly for my own projects, but with the eventual hope of writing some tutorials. While working on one of my running examples, I was encountering some difficulty expressing what I wanted in a reasonably declarative fashion. So I decided to see how it was done in Latin Modern.
I was dismayed to learn that Latin Modern is not a meta-font like Computer Modern. Instead the Type 1 versions of Computer Modern (which was developed by either Bluesky or Y&Y) were decompiled into MetaPost code as raw path outlines. So at that point all of the useful abstractions in Knuth's original code and specifications have been lost.
The only other major typeface developed in METATYPE1 that I know about, Antykwa Toruńska, has no source available and from the description I highly suspect that it was developed by creating raw paths that matched the scanned specimens. This got me thinking about whether there are any meta-fonts that have been developed in METATYPE1, or even whether Computer Modern might be the only full meta-font family in existence. I just skimmed through the METAFONT sources that are included in TeXLive, but didn't see anything particularly promising yet.
In any event, going back to the original issue, I have been starting to think that maybe the limitations of METATYPE1 are perhaps not worth being able to directly generate Type 1 fonts. It could be entirely possible that working in METAFONT and using something like mftrace to generate outline fonts from high-resolution bitmaps will produce results of sufficient quality. I'm hoping to do some tests to compare the two approaches this weekend.
(It is worth noting, that the comment about METATYPE1 on the mftrace page is slightly incorrect or out of date. METATYPE1 can handle overlaps, there are just complicated restrictions on how overlapping may occur. Finding clean approaches to avoid these restrictions was why I became interested in looking at the Latin Modern code to begin with.)