In another sign of openness, Microsoft has created a page where you can see which of the many standards it is planning to implement in IE. This is good - unless you happen to spot a missing standard that is vital to your project when it suddenly turns bad.
Microsoft does seem to be improving in its attempts to tell programmers where it might be going in the near future. There are still lots of areas where its silence is either worrying or puzzling - what about WPF for one and where is the replacement for XNA for another? However, if it is IE you are interested in then a new feature on the modern.ie website gives you a complete rundown on what is coming and what probably isn't.
The status.modern.ie page provides a list of features with a status of:
Implemented In - the version of IE in which the feature was first supported
Not Currently Planned
So to work out if IE is going to be a good modern browser and not cause problems you have to scan down a very long list. Most of the decisions are reasonable assuming Microsoft is allocating limited resources to IE development. Here's a selection of some of the more noteworthy.
Among the features Microsoft is working on are:
GamePad API, Media Capture and Streams, HSTS, HTTP/2, WebGL Instancing, CSS Transforms - preserve 3d, Web Audio API, Web Driver, Media Queries Level 4
The under considerationgroup includes some tags that the other browsers are working on and are W3C standards:
<picture>,<template> and <details> HTML imports custom elements
Other things being thought about are:
CSS Variables, SVG Filters on DOM elements, Shadow DOM, Canvas text decoration, masks, Web Notifications, SVG 2, MediaRecorder, Speech input and output, position:sticky, Service workers, Touch Events, File Writer, WebRTC-Object RTC API, Vibration API, URL API, Push API, Web Animations API, Ambient Light API, Battery API
Finally what they most likey will pass on:
MathML, Microdata, Quota Managment API, UIEvents, Web MIDI API, Web SQL, WebP, Web RTC v1 API
Most of the features in the under consideration category are W3C standards or drafts and either implemented or being implemented by Chrome, Firefox and Safari. What this means is that if "under consideration" turns out to be "not for a long time if at all" then these are areas where IE is going to lag.
It is also interesting that the IE team is still thinking about many APIs that are key to HTML web apps on mobile devices such as Firefox OS. If it turns out that things like vibration, battery, touch events and so on are not implemented then this will be a problem for web app writers.
One things that I'd pick out for special mention is that IE is getting Promises as well as some, but not all, ES6 features.
The biggest omission from near future IE is support for Web RTC v1 API. The other features being passed over are either niche or only implemented by one of the mainstream browsers.
For full information visit the site where you can also search and filter to find the feature of most concern to your future.
The site and all its data has been open sourced and you can download it from GitHub.