I also have tried to automate setting up “intelligent” default/initial values for Tasks when created from within a Rich Text field. The main problem for me is that I haven’t found a good way for a Rule to determine the context in which the new entity is created (i.e. the RichText and its containing entity).
I agree that it would be very useful to be able to prompt the user for more info situations like this, to save them from having to explicitly open the new entity and navigate through all its fields to find the ones that should be set. It is much more efficient if the user is simply presented with all the fields that need to be set.
If a “new entity created” Rule could be triggered/selected by specific circumstances of the entity’s creation – e.g. “Fire when a new Task entity is created inline in a Rich Text Field” – and if the Rule could also ask for user input like you suggest – that would be a neat solution. Especially if such a Rule also could use the entity’s creation context (i.e., in which Rich Text field it was created, within which entity). That context should actually be something that the Rule can test as part of its criteria; e.g., “only fire if the new entity is being created in a Meeting Notes Description field”. Then the rule could intelligently use the creation context to set up some default field values (e.g. assign the Task’s Project, via the Meeting Notes entity), as well as prompting the user for initial values like Assignee and Due Date.