I am not a developer, nor a librarian. I am one of the volunteers trying to piece together a logical set of relations between the millions of Wikidata items and, in the process probably reinventing the wheel again each day.
On the practical issue of the various 'levels' of works and what Wikipedia is doing about them:
Wikidata is already creating items for Literary works and separate items for Editions of those works (so that our citations can reference a page in a particular edition) and for individual books (because there a hundred or so individual copies of books which are notable enough to have wikipedia articles about them). Like you I am not clear what the difference is between 'expression' and 'manifestation' and which of them corresponds to an 'edition' so we may or may not already be using those concepts.
We have created specialist properties for linking works to editions which probably sort of match the properties in the FRBR document.
Note that in many cases however the wikidata item about the work also describes the first edition so I guess that doesn't comply with FRBR. That is unlikely to change unless someone comes up with a use case where it causes real problems.
Wikidata is starting to look at data items for free software projects. These are works which are all digital, probably never get printed. They tend to get updated frequently - often having daily updates. It will be interesting to see to what extent the properties and concepts for books are reusable for these works with their very different publication model. We are not trying to do this for wikipedia pages - we only link to the current page and we use a special type of property for that.
'Classes' in wikidata are not coded into the software - they are just items and are only identifiable by the fact that they are the subject of 'subclass of' statements. This means that creating new classes can be done by anyone at any time. Search well first though. It may already exist under a variant label. Search under the 'List of....' label too. Many classes are linked to 'list of' articles in Wikipedia and not all of them have had their Wikidata labels changed yet to reflect their class nature.
Hope that helps
Joe