Improve date/time selector

Rules Scheduler is kind of complex to explain without getting the whole Rules machinery too – but basically it goes like this:

• A "component" – a set of actions or conditions-and-actions – is created with the Rules UI. Each component can have any number of parameters, being the input with which it is evaluated. (The parameters could be nodes, users, text strings, and other data types supported by Rules.)
• Usually these components are scheduled from "reaction rules" – similar but more flexible than Drupal core's triggers. When setting up a scheduled component, each parameter must be specified – as well as the time for evaluation.

I would imagine the integration with Scheduled Actions like so:

• Rules components having at least one node parameter may be selected as actions for Node scheduled actions.
• When adding these components as actions, the time is set in the same way as for other actions – but any additional parameters are also configured. (This may or may not impose restrictions on which parameters can be used – providing a text string is much easier than, say, an array of user objects.)
• The scheduled components are treated as other tasks managed by Rules Scheduler, but also appear as tasks listed on the node form. (Scheduled tasks are available as Views objects, which might make this easier.)

I hope this kind of makes sense, and is possibe to understand.
A more in-depth integration with Rules makes sense to me too, and personally I wouldn't exclude turning Scheduled actions more or less into an alternative/additional interface for Rules. (The interface is pluggable.)

An introduction to Rules Scheduler can be found in this screencast, and more can be found here. Unfortunately they are only for Drupal 6, but the concepts are 90% the same in Drupal 7.

I hope to record a new screencast series about Rules in D7 before the end of the summer, but I have some other screencasts I want to record first. Hopefully I can have it done before GSOC is over. (Reading a bit more about your project I realize that you've spent some time with Rules already…) Good luck with your project!