This was implemented as tickets T224 and T2055. You can find more info there. Maybe not packaged yet. The feature is not enabled by default. You have to set $config['activesync_multifolder_blacklist'] = array(); in config.inc.php.
@aseigo sorry, to clarify, will CalDAV/CardDAV be the primary way of accessing Contacts and Calendar in Kube, with IMAP used for just mail, or will Kube continue to be Kolab-aware, and be able to support viewing all groupware data in IMAP?
As not overly technical, (and I'm not complaining) the advantages of having a single IMAP account which can store all data, except for the simplicity of setting up everything. Prior to using Kolab, which I love, I'd never heard of this concept of storing everything in IMAP.
Would it not be simpler for development and cost-effectiveif Kube simply did away with the ability to understand special Kolab IMAP, and just used IMAP for mail and CardDAV and CalDAV for contacts/calendars? I appreciate this is what you are trying to do by implementing JMAP, and this is awesome, and therefore makes Kube more useful to the world at large, particularly to those who don't necessarily use Kolab.