To me, the main reason why Slack and its bots will surpass Siri soon. With Siri dev being behind closed doors Apple has to rely on deep learning via the few possibilities Siri is doing rather good (text-messaging and directions). No further info about the context of the usage.

Slack in contrast gets the context of the user do to its various channels and interaction with others (human/bots/systems). Having that information deep learning algorithms will progress much faster!