To render UI elements that express the level of access to any one particular folder in a snappy fashion, we need to cache the desired representative state of each folder at the earliest opportunity.
For IMAP, this amounts to an ACI subject (the user logged in), and ACI rights that, in combination, result in to a read-write or read-only state for a folder. I believe we already cache this.
For Seafile, this amounts to a part of the response to API calls put forth to it, that is access level metadata. I'm not sure we already cache and/or use this.