* Sell Audio (Spotify, Audible, MP3 style): If the goal is to get into this business than you'll have much better reach if you sell on smartphones. The voice-assist app will be supplementary at best.
* Sell products (Amazon/Ebay style): People aren't generally comfortable buying products with voice-assist. You'll have to compete directly with Amazon.
* Market products (In-line advertising style): You'll have to generate a lot of original content to plug sponsored products. The original content will have to be very compelling. It's probably more appealing to host the original content somewhere else primarily.
* Sell audio advertisement: What make the voice-assist platform compelling for content consumption? How can you create a very engaging voice-assist app? Will people tolerate audio advertisements? They tend to consume more time and be less interesting than visual ads.