More platforms = more opportunities. The Kim Kardashian game on Android/iOS made $200 million dollars in 2014. You don't have to come up with a new niche to be wildly successful, you can innovate on execution.
That being said, I believe there is huge potential for new types of voice-only apps on the Amazon Alexa platform.
Yeah, there's a huge problem with discovery and new apps, though, which kardashian has a huge leg up on.
Other challenges are that people tend to spend 80% of their time on 3 apps, and that people are likely experimenting with new apps much less than they were a few years ago, as they've already got their goto apps at this point.
That being said, I believe there is huge potential for new types of voice-only apps on the Amazon Alexa platform.