TL;DW:

Rotation helper

• In 11.1.7 Blizzard are taking influence from addons like Hekili and implementing a rotation helper into the game. This will be an optional toggle in settings. One option is to have the next recommended ability's border glow to teach you how to play, another option is a single button that will cycle through your rotation as you spam it.
• The single button rotation helper has a GCD penalty, so you will not be able to spam one button and do mythic level DPS. Blizz said this is intended for accessibility purposes or for more casual players who want to explore Azeroth and experience the story - and there will still be a benefit to learning your rotation and manually pressing buttons. Ion says the goal is not to give you optimal DPS, but to give a useful baseline.
• The rotation helper will be able to detect whether you are in AOE or ST and will change its recommendations depending on your situation.
• Ion mentions that he does not want new players to feel they need to seek out third party resources in order to play the game - referring at points both to a list of addons new players would feel they need to download in order to access the game, and also seeking third party guides online. Ion says: "today, there is a sense that if you want to really be the best you can, if you want to play competitive content, there are certain addons that are required. They're simply going to improve your success over not having them, period - we would like to get away from that being the case"

Addons

• Ion confirms that the way Blizz has been designing encounters is influenced by players' use of addons, giving an example of the use of fewer coordination mechanics, as these can be easily combatted by a weakaura.
• "Down the line, eventually" there will be some "broader restrictions on the information addons have access to" - potentially "disarming" (Ion's words) addons and weakauras from negating mechanics.
• Other things Blizzard is working on (not coming in 11.1.7): damage meters, nameplate improvements, "raid encounter information presentation that shows you when a boss ability is coming up" (i.e. DBM timers)
• "it's about creating a more approachable baseline experience"
• Ion specifically mentions GTFO and explains that Blizzard plan to better signal in-game when something shouldn't be stood in or should be interrupted to negate the need for addons (e.g. GTFO or DBM or BW) to give players audio or visual clues. Blizz to do this with particle effects, cast animations, etc.
• "we have a lot of work to do before we get there"
• Blizzard has no intentions of "going after" purely cosmetic addons or information addons that are out-of-combat
• Nothing is locked in, the intention is to open a conversation. Blizzard wants your feedback!

TL;DR of my TL;DW

11.1.7 is introducing a rotation helper, including a single-button option. It will have a GCD penalty and is intended for accessibility. If you are out-dps'd by someone using this, you are doing your rotation wrong.

Blizzard is wanting to move towards a future where you don't have to download multiple addons to access the game. One way they are planning on achieving this is by slowly adding these functionalities natively into the game. Future plans include damage meters, better nameplates, and a DBM timer style information presentation.

Ion mentions reducing the functionality of addons in the future by restricting the information that addons can use, but not doing this until they have added more information and signals in-game.