Hi
Your reluctance is natural: beginning to implement a new standard when you invested so much time with the old one is heart-breaking. Furthermore, the two standards will coexist for the years to come. I am afraid nevertheless evolution cannot be stopped. Validating tools like Epubcheck are able to discriminate between Epub2 or 3 and check them accordingly.
I switched to EPUB3 some days ago as soon as my opensource software of choice for quite a long time allowed me to do so (with version 1.5.2. alpha). To concur with what you says, it does not bring me yet any additional capability. For this, I will have to wait version 1.6 which is still some few months away. Up to now, it's just a plain Epub2 with a new dress. This software can export odt files either to Epub2 or Epub3 formats.
http://sourceforge.net/projects/writ...r2LaTeX%201.5/
I find the transition to be smooth and the compatibillity to be good for example with my Kobo v. 2.8.1. which is quite an old version or with Prince PDF and the Calibre viewer. I did not have time however to make extensive tests on this field.
Comparing the files, I am just discovering some minor technical differences, hence my questions: the biggest ones are for writing metadata, others for .opf like the "properties" thing*, for the nav file and backward support for ncx, and that's nearly it.
I think it's a good way to join the fray. I feel I will be in a good position to implement later any new feature that could be of interest for me when they will appear, one at a time.
* when I tried to add a svg tag.