Not a Substack employee, but that would be tacitly endorsing users bypassing #3 — even if Substack doesn’t mind, their writers might. Safari is one thing, where it can’t be disabled. But going out of their way to add support for it in the app is probably a step too far.
https://imgur.com/a/PTwWor3
Adding that to the phone app would only be exposing it on the phone app - not hiding it from functionality for anyone who wanted to do it.