We hope to have a new Mattermost server available soon. I can't give a firm timeframe, although it should be in the batch of appliances that we publish. Fingers crossed, it may even be available this year. If not, then it will hopefully be very early next year.

In the meantime, you can either build it yourself if you'd like (i.e. using TKLDev) as the build code has already been updated and it should build successfully. FWIW we have a pre-release build that we're currently using internally so it should "just work".

Another option would be to manually update Mattermost itself. You can find instructions on the Mattermost docs. I haven't tested it, but a (very) brief scan suggests that it should be fine.

If you do do the upgrade yourself though, if you have any data in it, please be sure to do a backup prior to making any changes. That way, in a worst case scenario, you can get back to where you are now.

If you have any troubles with any of those options, please do not hesitate to post back with info and I'll do my best to help out.