If, at some time in the future, it manages to create a usable bridge to connect between two popular private services (say Whatsapp and Telegram, or Teams and Slack) it could start accumulating network effects, and become a desirable target for all other networks so that it is appealing for them to build their own bridges to the Matrix services.
Well, I think usable bridges for such apps are a thing already. See e.g. https://element.io/element-matrix-store and https://beeper.com
Problems are:
- it's a subscription based service
- End to end encryption is not active for these services as long as you don't run the bridge yourself (which in principle is possible as well, see e.g. the description at the website of Beeper) which stretches usable a bit...
Both problems would likely be solved if these services would provide an API for other messengers and would cooperate on a common standard for E2EE like MLS, however the likelihood for that ... seems pretty small. 1.
Using your telephone number as username the experience is transparent and unlike all other messaging apps. I can write texts to whomever and if they do have signal, it defaults to encrypted coms. It's inclusive by design.
Other services require usernames and email and whatnot, which effectively ensures it will not be the default. (I understand Apple users cannot change the default messaging app to only use Signal, which is a choice in tune with the walled garden and exclusive by design.)
What's a step forward in this regard is projects like libpurple or Matrix bridges. Whose goal is to make already existing networks interconnected.