How can I create a live updating slideshow?
Here is how you can do that in Power Point. I do not use Keynote.

There are two ways to insert content objects into a PowerPoint presentation:

Linked objects    A linked object is updated if its source file is changed. For example, a linked chart built from data in Microsoft Excel is changed if the source Excel data changes. The source file must be available on your computer or network to maintain the link between the inserted object and the source data. Inserting a linked object is recommended if the source data set is large or complex.

Embedded objects    The source data is embedded in the presentation. You can view the embedded object on another computer, because the source data is part of the presentation file. Embedded objects typically require more disk space than linked objects.