Planned for V2.
If a theme / plugin requires / depends on another plugin, show a note to allow/deny during install.
Maybe include a way to preset options/data for the additional plugin, e.g. if CF7 is required, auto-install it (if "allow" is selected) and provide/install custom premade contact-forms.
Planned for V2.
We'll need to implement this before we can remove basically any feature that plugins may depend on. For example: https://vote.classicpress.net/posts/4/remove-xml-rpc-specification
It's also a widely-requested feature from WP plugin developers who want to package utility code into a framework plugin.
Essentially: Bake TGMPA into core.
=> http://tgmpluginactivation.com/
Or, another option that Pieter pointed out in Slack: https://github.com/afragen/wp-dependency-installer
Or we could come up with a way to use composer for this.
An approach using WP-style plugin metadata is in progress at https://github.com/invisnet/ClassicPress/tree/v2.