That’s exactly the sort of use case we are focussing on and building our automated typesetting service for.¹ You’ll probably also benefit from file inclusions so that you can keep a library of text snippets, with variables, keeping them versioned separately, and which you can then re-use and assemble to form a new, slightly different manual, with the variables automatically populated at typesetting time.
Could you be more specific on the problem you’re facing with placing images? Is it that there are like hundreds of them, for which you would want to have created the references (and ) automatically, because typing out the file paths manually is too tedious? That is doable, although it would be more of a drag-and-drop feature to be implemented by a dedicated Markdown editor, or an ST plugin.
Or would you like to have more fine-grained control over floats, sizing and placement of the images relative to their place in the text narrative? For which a WYSIWYG interface is indeed more well suited, re: many document author’s gripe with TeX’s figure placement.