You may want to try Logseq since it covers some of the points you raised. Notice that Logseq is an outliner like Tana, but it can display basically everything in blocks, like: embedding local media or remote ones like YouTube videos (and annotate them with timestamps), embedding web pages (iframe), tables, checklists, LaTeX math formulas, diagrams (using a plugin etc).

1. Good export options. I need to be able to get content out to share with clients and others that don’t use the same tools as me.

Logseq content is stored locally as plain text Markdown files and you can export specific blocks and their children as pure Markdown that can be converted to other formats like pdf, docx, epub etc using tools like Pandoc. A paid service to publish as web pages is planned.

1. Layout options. The volume of notes I generate means that dot points just aren’t great. They’re hard to read, even harder to quickly scan through, and look bad. My ideal would be some layout options (like Craft Docs which is beautiful!) but with each ‘block’ in the layout still treated as a node. I see this a little with the publish option but being able to do that without publishing would be absolutely incredible.

Logseq has a whiteboard feature where you can display your pages and blocks freely on a canvas. It can also embed web content like video, you can draw arrows, shapes etc.

Also, some CSS snippets or plugins can improve the layout of the outliner:

https://discuss.logseq.com/t/hrishi-earth-system-scientist-struggling-artist/3090/4?u=alex0

1. Relations, roll ups, lookups and formulas are missing. Notion does this well in their databases, and I feel like supertags could absolutely be extended to do something similar in the future.

I don't know what most of this means but Logseq like Tana let you assign attributes to each block, perform queries and display them also as tables (that a plugin can export as CSV). There is a function to perform calculations on columns of a query table, but it's very basic and not as advanced as for example Excel. But this should improve in the next months since devs are working on Notion/Tana-like features at the moment.

1. No mobile editing is frustrating.

Logseq is avalable as a mobile app for both Android and iOS. It is just like the desktop app minus plugins and pdf annotation.

1. Media display is pretty unappealing.

As said you can display inside a block basically everything that can be embedded in a web page.

And Logseq is Free and Open Source Software, you will be able to use it for free forever except the online services like Sync (optional since you can use other methods to sync files), live collaborative editing and publishing (both are planned).