We’re working on building an IDE of sorts [1] (but specifically for tasks/notes) trying to combine the benefits of plain text but with rich elements and structure (tree/graph). The illusion of a real editor breaks down pretty quickly when you can’t easily copy-paste or select rich elements as if it was plain text, so that’s why we’re trying to build the whole thing from scratch.
Thymer has real-time multiplayer with CRDT based synchronization. With org-mode you can collaborate, but you'd have to DIY with git or something similar. Thymer is also end-to-end encrypted. With org-mode you'd have to self-host something to sync with your phone.
Org-mode is text based, Thymer has a document graph. Advantages of the graph approach is you can nest as much as you want and zoom in on any part of the graph. You can transclude sections and have references and backlinks. With text based approaches you have to sprinkle location identifiers (guids or relative paths typically) into your document so you can track the location as files gets edited. But guids are awkward and paths can result in broken (back)links. We built Thymer as a document graph from the ground up. Tree mutations don't break (back)links.
With Thymer every node in the graph has metadata. Who last edited it? When? Where did it move from? Previous versions? For text paragraphs this isn't super useful, but when you have tasks this metadata is very useful.
org-mode on a phone? I'm sure there are apps for that, but I think it's designed with a keyboard in mind. Thymer uses the (subjectively) more modern command palette approach where you don't have to remember as many shortcuts, and it also translates more easily to touchscreen devices.
[1] https://thymer.com