Dailies
Have daily/weekly/monthly/lifetime achievements for viewers
eg.
Dailies
"Watch a streamer not in your follow list"
"Participate in a Raid"
"Chat in a stream"
Weeklies
"Watch the same streamer on 3 different days"
"Watch a streamer not in your follow list (3hrs cumulative)"
"Participate in 5 raids"
"Gift a Sub"
Lifetime
Become a Top Chatter
Examples of rewards:
Trading Cards
Achievement Points
Achievement Points redeemable for things like special Username colors
Profile Badges
Exclusive Global emotes (eg Platinum Kappa)
Special Login Events rewarding Exclusives (badges, seasonal emotes, variant global emotes)
Lootboxes with similar rewards
I'm just idea throwing but we're all gamers at heart, dailies would be very congruent to Twitch culture.