I also noticed a slight change coming from 4.0.7 app tests I had to get them working in 4.2 but it wasn't much on my end. Changes for 4.2.0 is commented.
Here is a snippet of my 4.0.7 arch-app.js:
And here is the same under 4.2.0 Beta 2 (I haven't tried the nightly yet):
My directory structure is below:
//Added the /js-4.2.0 to the relative path from the current html page location.
//My arch-app.js is in js-4.2.0 directory but the html page is located in the parent directory.
//Added the ./ in front of this path so it's relative path from current html page location.
Of course I only use dynamic loading on the local machine for developers. We are currently building the sencha cmd into our build process using ant. But this is all I changed to get it working for me. If yours is working with beta 2 let me know and I will update ours to the nightly build to see what the difference is.