Sadly, now it's getting harder and harder to run applets. And I'm not going to code a different web-based version of my system (which would involve not only rewriting a lot of code, but finding different libraries to handle MP3, OGG, SVG graphics, etc.) so I suppose my system will just slowly fade into obsolescence.
For some things, applets are still the best choice... or would be, if users were not aggressively discouraged from using them due to what amounts mostly to PR campaigns (as i.e. Flash is by no means more secure than Java applets, and browsers don't make you click through four layers of scary dialogs to run it).
What I hate about coding projects for end users that need to run on shiny platforms (like the web) is that you always get caught on politics. Stuff like company X not allowing running software written in language Y on platform Z so as to promote its own platform, and making you port everything several tiems. Or company X including a crippled distribution of software Y because it hates company Y (this happened with Ubuntu and Java and has brought me scores of bug reports to handle). I guess my future hobby projects will be in C/C++ and directed to technical users that don't expect to run their machine learning software (for example) on a tablet browser...
Of course, you could always use C/C++ with emscripten, and target the web that way...
With Java on the other hand, I had a desktop app and an applet sharing the vast majority of the codebase, only very specific parts of the code (a small part of the UI and I/O code) differ. This is what was allowing me to maintain the project and support both desktop and browser, until the applet paranoia growed out of proportion and browsers put applets in permanent quarantine.
Of course, if I started this project now rather than in 2000, I would probably make different decisions regarding language and technologies used. Although it would still be a bit annoying not to be able to use Java. It's not my favorite language, but I definitely prefer it to JS by a mile.
I agree that re-writting an app of that size is a giant PITA.
You could always use GWT though, and compile Java to Javascript. Altough you would probably have to re-write code as you're not targeting an applet anymore.
But yeah, at least I could try and see if I can get a subset of the system working, even if it's only to learn some GWT :)
No sane Java developer would start a new project with Applets.