I think the only option here would be writing JJ2 engine from scratch. Most of, if not all, fileformats used by JJ2 are fairly well documented, so it'd be good to do it. There are several advantages of doing it this way, actually:

- Engine, written from scratch, would be 100% legal in itself. You still would need JJ2 data files which aren't legal to download, but you could make custom campaign with custom sprites to satisfy people who don't have JJ2, still completely legal.
- Would run on many different systems and architectures if written properly, not just Window$ x32
- Greater control over engine's capabilities and easier way to remove any limits of it (admittedly easier than hacking at JJ2 executable in assembly, like it's case for JJ2+)

Of course this would need more work, but there are frameworks that take off most of coding needs, like rendering, collisions, etc. SFML, libGDX - to name a few. So it's not that you'd need to write everything and the kitchen sink from scratch, unlike original devs of JJ2

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