Bulk channel selection for Slack Broadcasts

We have over 600 customer Slack channels that are connected into Intercom via Workflow and via that integration. 

We find it really useful to use broadcast to notify customers of feature updates or important changes to our platform using Slack broadcasts. But right now, we're limited in this because the only option to segment which channel should receive messages is based on a dropdown with a checkbox beside each channel name. It's really inefficient for the volume we're operating at. Ideally, we would be able to segment directly in the broadcast itself and add details related to those Slack channels, potentially by associating it to a company record. The simplest solution I see in the meantime is having an upload-a-CSV option that could then select all of the channels that are included in the CSV.