Just to add to Jamie's answer. There is nothing that stops you from building skills for Echo Buttons using the older Alexa SDK. In fact the earlier samples for Hello Buttons (https://github.com/alexa/skill-sample-nodejs-buttons-hellobuttons/tree/alexa-sdk-v1), Color Changer (https://github.com/alexa/skill-sample-nodejs-buttons-colorchanger/tree/alexa-sdk-v1) and even our Trivia Template (https://github.com/alexa/skill-sample-nodejs-buttons-trivia/tree/sdk-v1) are all built using the Alexa SDK.
The new Alexa Node JS SDK brings some improvements and there are good reasons to use it if you can but if you have a skill built on the v1 Node JS SDK you can still add support for Echo Buttons to it by following the examples I linked above.
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