IE11 supports dragging files from the desktop/File Explorer to upload to for example OneDrive or other sites which use the HTML5 file upload API and support drag and drop.
This doesn't work in Edge. This is a quite serious regression.

Now text-combine-horizontal renames text-combine-upright.

-ms-text-combine-horizontal property
https://msdn.microsoft.com/en-us/library/dn337005%28v=vs.85%29.aspx

9.1. Horizontal-in-Vertical Composition: the text-combine-upright property
https://drafts.csswg.org/css-writing-modes/#text-combine-upright

Specification: http://lars-t-hansen.github.io/ecmascript_sharedmem/shmem.html
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Enables atomic operations on shared memory locations. Allows for the role of "threads" to be played by Web Workers in web browser environments.

Use cases:
- Support for threaded code in programs written in other languages that are translated to asm.js or plain JS or a combination of the two, notably C++ but also JVM and CIL bytecode, Halide, Clojure, Rust, and similar safe languages.

- Support for hand-written JS or JS+asm.js that makes use of multiprocessing facilities for select tasks, such as image processing, asset management, or game AI.

Add ability to dock Developer Tools to the current window.

Please UPDATE your WebDriver module for Edge and support XPATH and other missing identifier functions, etc., so we can run the same scripts to test Edge in the same way we test other browsers. You say you are going to support it, but if you don't update it, that's not supporting it.

Support .remove() method on DOM elements

https://developer.mozilla.org/en-US/docs/Web/API/Cache

Please provide a VM for MS Edge browser on Win10 so that we can easily test web apps.

webkit currently supports the property background-clip: text that can be used to create awesome text filled in using background images, gradients, ect. Its an incredible feature with so many possibilities and I'd like to see supported in other browsers.

Add support for SharedArrayBuffer :
http://lars-t-hansen.github.io/ecmascript_sharedmem/shmem.html

These basic form validation types is still not supported on IE, even on Edge, whereas they are supported by competing browsers like Firefox and Chrome.

<input type='text' pattern='[input your validation here]' />

OR

<input type='text' required />

That will be very useful as we don't need to use server-side coding and even JS coding.

Please support the Theora video codec since video servers such as Wikimedia use this.

http://w3c.github.io/preload/

http://www.impressivewebs.com/html5-form-attribute/
would be nice to use that feature, IE seems to be the only browser without support for it :)

element.runtimeStyle is non-standard, unnecessary and unintuitive.

- It doesn't match any standard or any other browser.

- We already have the `style` attribute on elements.

- If I clone elements with any runtimeStyles set then the clones also get the runtimeStyles. But if I copy the elements using an `.innerHTML` (or similar) approach then the runtimeStyle is not copied.

Implement extended srcset which includes support for the sizes attribute on the image tag and the addition of the width descriptor instead of just the pixel density descriptor inside of the srcset attribute.

Download of virtual machine on dev.modern.ie is not possible. There is a javascript error (i18n is not defined). Please debug it. Thanks

Edge should prevent a page from repeatedly popping up modal dialogs that block action on the current or other tabs. In IE 11, it is possible for a page to pop up a modal OS dialog window, and upon attempting to close that window, simply re-open it. I experienced this today with a rogue fake virus warning page, and had to kill the entire IE process to get rid of the dialog. Simply unacceptable from a security standpoint.

http://dev.w3.org/html5/spec-preview/textFieldSelection.html

I used to use the el.createTextSelection method to determine the selection direction in IE11. However, inputs and textareas no longer expose this method, while still the el.selectionDirection = undefined.
We don't have any way to determine selectionDirection now.