Aggregate calendar view has been suggested before (https://twitch.uservoice.com/forums/928429-channel-page/suggestions/46080367-combined-schedule-for-viewers), but I would like to expand on the concept and offer additional ideas aligned with Twitch's goals.

THE ISSUE:
In my experience as both a Twitch viewer and streamer, the schedule tab is extremely underutilized.
Because it is only accessible on an individual streamer's channel, it is inconvenient for viewers to actually access.
As a streamer, I have very little incentive to utilize the schedule feature, because most viewers do not know it exists and/or think it is too cumbersome to access. Those viewers rely on off-Twitch methods of knowing streamer schedules.

PRIMARY PROPOSAL:
Primarily, I propose an easily-accessible aggregate calendar view (it can be expanded from a collapsed menu on the front page, permanently displayed on the front page, or be a new page linked from the front page) that shows a user all of the streams scheduled by channels they follow.
Filters will be needed for users following many channels, but default sort could use the same data as the "Recommended" sorting of live followed channels.
There should also be an option to toggle on/off the visibility of recurring unnamed streams vs scheduled streams with a game/title.

Featuring this information to viewers would encourage streamers to actually fill out their schedule information, and it would encourage viewers to stay on Twitch more often as they know when their favorite streamers will stream.

SUPPLEMENTAL PROPOSALS:
Suggested Stream Times via Analytics
Additionally, this data could be used to make suggestions on when to stream in a streamer's analytics. This is aligned with other features Twitch has added, as channel analytics already suggest other streamers to check out as well as categories to stream, based on who/what your audience watches.
Analytics could suggest new times to stream based on when their audience is online and at times where many others aren't already streaming.

First-Party Calendar Management Plugins
There are currently third-party plugins for Google Calendar that help make it easy to add events to the Twitch Schedule from Google Calendar events.
An official Twitch plugin for this would encourage streamers to utilize the scheduler more. Additionally, you could have a tool for viewers that syncs a streamer's Twitch Schedule to a viewer's Google Calendar (or other calendar management service).

Overhaul of Schedule Tab on Twitch
A condensed/simplified schedule view could be added to the About channel tab. Many streamers already use a third-party panel extension to display their schedule, but a more officially-integrated option would encourage more streamers to use the built-in schedule feature. It would also free up slots for streamers to use other unique panel extensions.

In conclusion, I think these features would encourage streamers to be more organized and consistent with their stream schedules, and it would encourage viewers to spend more time on the platform. It would benefit both streamers and viewers, and encourage usage of existing-yet-underused features like the schedule.