The way I look at the issue of MODS vs. MARC is since the vast majority of library records are in some type of MARC now, it is a matter of what is lost vs. what is gained with switching to MODS.=
1) the map from MARC to MODS is at: http://www.loc.gov/standards/mods/mods-mapping.html#mapping, and it is clear what semantics are lost. My previous example were the different subfields in 130/240 being lost when mapped to MODS <title type=uniform>, specifically the $s. Again, the information is not lost but the semantics. There is also 111, 711 $a$c$d$e$n$q, but others as well. There are certain concerns I have as well, e.g.
245 $a$f$g$k <title> with no <titleInfo> type attribute and
245 $b <subTitle>
which is rather strange from the logic point of view (e.g. 245 $g is for "bulk dates" which I believe are primarily for archival materials, but as a result would semantically mix together dates of creation with title information). I don't believe I have ever used those fields before, so probably the issue would arise relatively rarely, and yet I may be completely wrong! In any case, this mapping makes clear what would definitely be lost when transferring a record. Whether that would be seen as serious or not needs discussion. MODS could be further modified if some bit were deemed sufficiently important.
At the same time, Ashley decided that MODS granularity was too fine.
It is also important to remember that this information is lost *onlY* when transferring the record from the database.
What we would gain by changing to a more normal type of XML format does not have to be discussed to this group.
At this point, the whole discussion may be moot because of the latest worldcat record policy. I still haven't made up my mind. The section
"WorldCat Data. For purposes of this policy, WorldCat data is metadata for an information object, generally in the form of a record or records encoded in MARC format, whose source is or at one point in time was the WorldCat bibliographic database." seems to claim as Worldcat data a record of 040 $aDLC$cDLC$dMyLibrary, if it was downloaded through Worldcat. If I downloaded it through direct Z39.50, it may be another matter, but I may have to prove that somehow. Again, to me it's like taking my car to the mechanic, I pay him to do some work on my car, and then he claims that I can't sell the car or do anything with it without his approval. And why? Because if I do so without his approval, it may hurt the "local collective" in some way.
It seems to be a done deal however. And I find it amazing that people have gotten so concerned about Google Books!