Hi Benny,
i try your solution and the yellow background is visible for a blink of an eye and the first page is done loading and visible for the user, meaning for the most part of the loading process the page was white...
said that, let me share you with my thoughts, i'm having other things that drives ME crazy so feel free to take it too from here if you feel up to it.
as i see it, the main problem is that for a web app, a quick user response is a must so most of the small/mid JQM projects are set to "Render all pages in one HTML file (jQuery Mobile multi-page template)" and in such way since all the project is cashed in your mobile it has better response however the cost of it is that we need to download ALL the project as a whole and that takes time until all is downloaded and ready... and on that same time we want the splash screen to be visible, so, if we to set the project as "Basic single page template" the first page will load quickly, and what it does is run a serious of the following code (as many pages that inside the app):
code
<a href="mainPage.html" data-prefetch></a>
<a href="FAQ.html" data-prefetch></a>
<a href="loginPage.html" data-prefetch></a>
/code
that way the splash will be visible all the time while data-prefetch run for each page that will be cashed locally for the user to keep our web app responsive as if it was a multi-page template.
IMHO the POC needed is to get the current state of the data-prefetch in such way that it will be translated to percentage.
if POC is viable, then, all is left to do is to show the first page (that should be cashed quick as it base on the "Basic single page template"), a timer that will query on the current state of the cash progress and update/refresh the progress bar for the user to know when that awesome app is ready for him.
thats just my two cents
Best,
R.