Are there any plans to add something like this to Alexa or Cortana? Shoot, get it on Bixby for Samsung..
Nope, no plans to program a bot for these old failing platforms.
lets be honest here, has relatively low adoption for non-trivial tasks.
Do you have a source for the lack of 3rd party bot use? It'd likely be because the Google Assistant is still in its infancy & the competition has several years on them. Give Google a year or two and a few hundred million more users will be using the Google assistant.
I think, as it comes to bots, we are just breaking into the mind-share of consumers and haven't even scratched the user base possible, yet.
Yeah, most people either don't have access to a bot or they're unaware that they have the functionality available to them, but that's changing every day.