Are there any Final Cut Pro, Motion or Premiere plug-ins that allow insertion of PowerPoint or Keynote slides?
If your show requires some level of postproduction, then:

1 Record the live video feed of the presenter's slideshow.  Don't just export the slides as a movie from Keynote.  Syncing slides manually will definitely keep you up into the wee hours of the morning, so don't do it.

2 Import the camera feed(s) of the speaker, any extra audio sources, and the slides, group them in a multicam clip, and sync them all together.  Again, for fastest postproduction turnaround, the more automated you can make the sync process, the earlier you get to go home.  Timecode based sync is the fastest, but most expensive.  A hand clap is free, but won't help you sync the slides to the speaker.  You've obviously already figured out how to do that manually, but finding one sync point per hour of footage is way better than doing it for x number of slides.

3 Once you've been through a couple of episodes of your show, and ironed out the kinks in look dev and process, save an extra copy of your project file and strip it of reference to any of the media you imported in step 2.  Leave everything else about this file alone; titles, intros/outros, etc. Use this file as a template for your show.  If your process involves complex file hierarchies, do the same with your file hierarchies: have a "template" project folder which includes your project files, working directories, output directories, stock graphics, etc.

4 Now, each time you do a new show, duplicate the template structure, rename it accordingly, populate it with your fresh content, fill in the blanks, and start over at #1.  As you work through more iterations, tweak the template files to incorporate as much repetition as you can automate.  You might want to pick up a scripting language or two, maybe look into some machine vision algorithms, keep an eye on github. Automate anything that gives you carpel tunnel.  Reschedule every progress bar you see to a time when you won't see it.

But if you don't need to make any kind of postproduction edit, then the answer's simple: Don't.

You've now left the world of digital film production and entered the land of broadcast.  To pursue this avenue, you'll need to be able to mix and switch all of your live a/v, and record or OTT the program.  Your requirements are minimally a $100-ish converter box and a laptop, but again, the more money you can throw at it, the better.  Blackmagic ultra studio mini recorder or whatever Aja's equivalent product is called would get you started.