In short: Amazon has introduced Whisper Mode for Alexa, allowing you to whisper to Alexa and she will whisper back to you. Now the feature isn't yet available, but it will be available in US English next month. Amazon is also presenting a paper on this at IEEE Workshop on Spoken Language Technology in December. The reason for this is because Amazon had to put in quite a bit of work to get Whisper Mode to work on Alexa, and that's because whispering is much tougher to decipher than simply talking. Not only because it's quieter, but because you are not using your vocal cords. So that Alexa couldn't rely on the typical voice signals to use Whisper Mode.
Background: Whisper Mode is actually something that has been highly requested by consumers, and that shouldn't be a surprise. If you wake up early in the morning before everyone else, and want to find out the weather, or the news, you don't want Alexa shouting. So this way you can whisper to Alexa and she can whisper back the answers to your queries. It's likely not going to be a really big feature for most people, unless you have a newborn child in your home, then it will likely become the standard way of using Alexa.
Impact: This could lead Google and even Apple to create Whisper Modes for their assistants as well. Though it would be surprising if Google was not working on this type of feature for Google Assistant already. But as Amazon has found out, while creating its Whisper Mode, it's not an easy feature to implement, and it actually needs to be done for each language. So that Amazon can't just simply roll it out for all languages that Alexa supports currently, it needs to roll out each language individually.