This is a great wish list.
Some things you can already do:
A dummy install in the debugger. Don't want anything actually installed just want to be able to walk through the Install flow. Like the old WiseScript debugger.
Easy to mimick - just comment out Apply Install/Apply Uninstall.
Disable Uninstall completely
Just delete the registry entry for your product in Add-Remove Programs, and of course do not create an uninstall shortcut. You will also want to adjust your script so it doesn't offer a path into Apply Uninstall - but I guess that much is obvious.
Some clarifications:
WebMedia 7ZIp file names should match the name of the file in the media block URL entry
Since you can enter multiple URLs, this really isn't possible. The 7ZIP file name is generated based on the web media block name, so you can just rename the media block.
Always overwrite file setting.
This is technically not possible with Windows Installer. You can use the Delete Files Recursive MSIcode command to forcibly delete files before installing them; we are open to suggestions on how to handle this in other ways (given that MSI cannot support this natively, it will be a custom solution).