Motivations
Selection actions are a nice way to keep the feature while reducing controls surface. However, it requires a native component and thus will not be prioritized.
Describe the Feature
An illustration is better than text.
Bellow is an example with Telegram application:
Android

iOS (3 steps)

Possible Implementations
This feature requires a rewrite of TextInput.
Android
On Android, the ActionMode it the preferred solution, of type ActionMode.TYPE_FLOATING. This type is only available from API 23 onward.
Telegram implementation relies on an extended EditText which reacts to ActionMode events.
The extended class is org.telegram.ui.Components.EditTextCaption
EditTextCaption::overrideCallback is responsible for registering different hooks on ActionMode events. This method is called in overridden startActionMode methods to decorate the callback and react to these events.
iOS
On iOS, the implementation should rely on overlay views applied to UITextField.
TODO: inspect Telegram iOS implementation in repository: TelegramOrg/Telegram-iOS
Windows
No support scheduled ; suggestions welcome