You could provide the framework that well-behaved, maintained programs will use while still allowing the old installers to run. By the way that's what we have

You could provide the framework that well-behaved, maintained programs will use while still allowing the old installers to run. By the way that's what we have on Linux, some programs come as a shell script that you run to install them. Most Java IDEs for instance. (which can't be arsed to provide proper packages -- darn, what did I just write? :-))