Hi Dr Rob,
Sounds like a fun idea.
The easiest way might be to get a home automation switch that when called will simply connect the two wires of a e.g. Powerpoint slide switch together forcing the next slide.
I'm working on an application that could fire off the next slide based on a mixture of commands that you'd set up yourself,
Alexa, When you're ready
Alexa, Next
Alexa, come on love
I've already got Alexa to perform searches across 4 different search engines simultaneously and then drop the results onto 4 separate monitors e.g. Who is Tom Jones, results in,
Standard google search of 'Tom Jones'
Google image search of 'Tom Jones'
Wikipedia search of 'Tom Jones'
YouTube search of 'Tom Jones'
all within a second or so. Commands also allow for Alexa to trigger applications and quite possibly application 'Powerpoint' slide switches instead of hardware ones.
Video to be released soon. Will try and test of your idea of slide switching too.
Jez.