My clients never knows how to create a mailto: or tel: link - would be great with a little help, when they create links. Maybe just a text explaining it, or small buttons for adding the prefixes.
This is not added yet, you might have seen that we are rebuilding our page builder at the moment, and i took care to forward the message to the team for them to consider and prioritize.
This is not at the top of their priority at the moment (They focus mainly on the Media library and support of granularity of roles) but they recently passed improvements to the link field allowing you to create relative links and anchor link.
It's a step on that direction and you can expect that more improvement like the one requested will come.
Thanks for your understanding and patience on that matter.