Will version 3.5 support encrypted DOCX or XLSX files generated by MS Office 2007/2010? In the current available version (RC3?), these files are not recognized by Calc.
Short answer: no - once a release is out, new features are not added to it.
There is a bug reported about this for LibreOffice 3.4 (#fd35422). Please subscribe to the bug (unless you’re the reporter). You can also bring attention to it via forums, social networks,etc., however reverse-engineering or even implementing features from other formats (even from documented sources) may take some time as other priority tasks may take the existing resources already.
Also see:
The latest update for fdo#35422, on 2012-12-21 by dev Kohei Yoshida:
“I’m turning this into an enhancement request. This is not a bug; it’s rather a missing functionality. Excel 2010 uses different encryption method than that of Excel 2007, and we’ll need to write a new handler code for this.”
fdo#35422 – Status: RESOLVED FIXED