I'm terrible in visuals. I rather provide the raw content and someone else makes it beautiful.

For a team page that's pictures of the team and their roles.

For a product it is pictures from my product designer. Or specs that might be put in a nice looking table.

For user scenarios it is photos again, but with a caption. And yes, if I do it myself that caption will look ugly.

So text templates are super useful to me. I'm also much better in using icons than designing them. :-)

It is not that hard. You just have to refrain from some dangerous features like colors and different fonts.

http://beza1e1.tuxen.de/slide_design_programmers.html

I think it should be both.

The best example I can think of is the WPF IDE in visual studio, where you have markup and GUI side by side. You change one, it updates the other.

Most people would edit slides in GUI mode only as they currently do.

Pros would spend a lot of time in the markup, which would enable much faster formatting, copy pasting of certain properties, manage invisible items, add meta data to text (like bind this word in that paragraph to a cell in that spreadsheet).

That how powerpoint should evolve if it was still under active development.

Also think of this use case: generate a powerpoint deck automatically from a system. You definitely want to be able to edit your markup for the template, and be able to generate markup from code.

In ideal conditions yes, but many presentations are not in such. Favorites include talks in over-filled rooms in noisy environments (not everybody can hear the speaker properly) and presentations to bosses or professors who judge your presentation by what they think when they look at the slides two weeks later, not remembering a thing of what you said.

This could at the very least be useful to get the initial text on the slides quickly, while still allowing you to fine-tune them in the GUI afterwards.

"...should be visually appealing"

I would claim that's highly context sensitive. If the goal is to share information in an environment that has keen interest on the content of the presentation the visual appeal is of a tertiary concern at most.