We need an estimate of the messaging traffic volume (on average and during spikes) that the push infrastructure will need to handle. This will depend the number of users expected to opt in and the kinds (and frequency) of events we need to support.
- Android active devices (as of 09 Mar 2020): 7.7M
- iOS montly active users (as of 18 Feb 2020): 3.8M
- Expected opt-in rate (iOS): 43.9% 
- Expected opt-in rate (Android): ~50%
- Pageviews (Feb 2020): 20B 
- Edits (Feb 2020): 44M 
- User edits (non-bot) (Feb 2020): 21M 
- Expected opt-in rate: ~10%
- The volume will depend on how many users we decide to prompt, which will depend on in what situation(s) we do so.