Feature summary (what you would like to be able to do and where):
This new parameter would be similar to to preload= with the difference, that, instead of loading content from a separate page, the content can provided right after the parameter

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

• When the content to preload is very short
• An alternative way to preloadparams[]= when you need to do more complex stuff that you prefer to do where you have the needed variables in context or want to use named values instead of numbered ones

Naming considerations

• preloadtext=/preloadraw=: Might be interpreted to imply plaintext only, which might be what is supplied but usually not the content model of the page it is preloaded in
• preloadwikitext=: Might be interpreted to imply wikitext only, which might be right in most cases, but there might be pages with different content models, even though afaik, JS, CSS, and JSON(?) pages cannot be preloaded

Benefits (why should this be implemented?):

• Better overview, because everything is in one place
• No cluttering with templates for one-liners
• No (at least not necessarily) alternative syntax for parameters