Just to relate my own experience, we started our forum with lots of categories and subcategories, but after a year, we’re actually moving in the opposite direction – eliminating subcategories in many cases and using tags instead. I’ve found tags to be far more flexible, and their use surfaces content that users might otherwise miss by not looking in the “proper” category or subcategory.
Just something to consider!
Have you considered using tags to structure things beyond the subcategory? It’s something that works today as-is.
AFAIK there are no plans to go beyond subcategories, it has been discussed many times and the benefits just aren’t there.
It is a long story but we will be adding three levels as it comes up too often for enterprisey clients.
To me it is a clear case of “be careful what you ask for” but then some people willingly eat blood sausages, so… 
Those are delicious 
Jeff,
that is excellent news. we have thought long and hard about using tags, but I believe three levels of nesting are the right solution for what we wanna do (especially since categories do up-merge, i.e. the parent shows all posts from all its sub categories).
Do yo have a (guesstimated) time line? I know you cant make any guarantees, but are you thinking in terms of next week, next month, or next year?
thanx!
marc
Somewhere between next month and next year, but you can certainly make it happen faster by signing up to a enterprise plan with us 
Is there something comparable to that for self-hosting? we’re not really in there market for stopping to self-host, but that doesn’t mean we’d not be open to financially (or otherwise) contributing…
We occasionally take sponsorship for big features if we know we want to build them just can not justify cost at this second.
But fair warning, this would be expensive to sponsor, we are talking about 2-6 weeks of work at our current hourly rate. If you have budget to sponsor the whole thing, sure you can contact us at team@discourse.org
Gotcha. that’ll probably be a. bit out of the scope for the project we have this in mind for, but we’ll take the option under consideration… Thanx!
any idea on an ETA on this one ?
It is still on the same state:
Raising my hand for this feature, please.
We’re actively working on this at the moment. It will likely be available in the early new year.
Oh, snap. I finally just convinced myself to switch to tags. This is an emotional rollercoaster. 
You’re better off with tags. This is basically the “I enjoy hitting myself” site setting when enabled.
How would I use Tag instead of a nested sub-category?
How is this project coming along? We’ve been using tags since the beginning however I find that a third level would save me headaches and work for a specific use:
note: on our site categories are referred to as channels
Two channels serve the core purpose of the site and purposely do not have sub-channels but use tags extensively.
All other channels exist to fulfill a complementary function : feedback (site and community meta communication), announcements (historic and chronological repository of all outgoing communication), in the news (« Out there » news related to our purpose), Resources, Reviews, HVAC (a venting non moderated spot accessible only to subscribers which topics are not displayed), etc.
Really, these top channels could be tags but I want their topics segregated from the rest as they have specific functions that belong in separate « forum sections ». Unfortunately, because the top level is used to provide a « section title » for the group of related channels it contains, it is currently impossible to have sub-channel
Use case example:
In « Ressources » we have ‘books’, ‘training’, ‘sample files & code snippets’, ‘Apps (free offered as is to the community)’, Products &Apps for profit, 'Plugins’…
Plugins are such a big thing with the platform we use that it justifies its own channel. Especially to segregate them from the actual products that are produced using that platform.
Some plugins creators are actively marketing theirs and I wanted to avoid having a few different plugins threads lost in tons of « updates, announcements, releases etc » threads by those active promotors. So, I created the rule that there can only be one thread per plugin. Aside from the fact that people need to be constantly reminded, i end up having to constantly clean up that channel.
If I can create a sub-channel per plugin, I can let each developer/product promoter take care of their channel, have promos, updates announcement yet limit to one the number of threads displayed for that specific plugin channel.
So I am really looking forward to the ability to nest one more down!
The next super useful functionality would be to have « channel (category) » level moderators. Being able to give moderation rights to only specific channels would be awesome.
Currently my work around is to create a group named JohnDoe_curator, make John Doe owner of the group and, for the JDcollection channel, give creation rights to JohnDoe_curator group and reading and replying rights to Everyone.
Hi Cécile – it was completed a couple of months back but on our hosted plans it is only available to Enterprise customers.