There is no information for Zimbra customers about the future of Briefcase vs Octopus, nor how it will affect them and their deployments.
Paying customers need to make long-term plans, and expect at least a solid indication of whether major features will continue to be available.
Please can VMWare set-out for your users (here or in a blog post) whether:
1) is briefcase is being deprecated, and scheduled for removal in Zimbra 9?
2) is Octopus going to provide a drop-in replacement for briefcase?
3) will Octopus be available for opensource users?
4) will Octopus be available and installable for basic Zimbra Network or opensource users (i.e. those who have a single installation, who don't want or need Horizon etc...)
5) if so, will Octopus be an extra cost on top of the current Zimbra licence?
6) will Octopus be installable within/with Zimbra, or will it require a separate hosting environment?
7) will Zimbra tags and email attachments be shared/shareable with Octopus?