This is a known limitation, and this functionality was put into place to stop Out Of Memory issues from happening when diff'ing very large documents.
For the short-term, I do not see this changing as to keep our system stable. However, if there is a big enough demand to have large documents to do a version compare, I would say we can revisit this issue then.
Please let me know if you have any other questions or concerns. Thanks!
I'll give a concrete example: A List of Tips and Tools for using Unicode in LabVIEW. I read this document for the first time early last year, and since then it's been revved 21 times. I would like to be able to spot new information if new revs are introduced, and that task is easy when performing a diff.
The PDF of that document is only 109kB, and the uncompressed text portion is around 20kB. This does not qualify as a "very large document" for conventional diff tools. What's the document size limit the current system can handle? What would constitute a large enough demand to revisit the issue, and how involved is the solution? This is a really cool feature that I would love to use, but it currently doesn't work on many interesting documents on the Communities.