KDevelop 3.5 development should happen in KDE/3.5/kdevelop, the KDE3 release maintainer doesn't oppose small new features and one or two changed strings (see kde-release mailinglist for the KDE 3.5.8 release thread).

If anybody has larger changes that he wants to do he can open a feature branch and if its done we can discuss merging the changes (or not). Keeping both branches in sync is doubling the "everyday" bugfixing work we can easily avoid with this.