It suggests that the four giant planets of the Solar System roughly formed where they are now. If they have migrated, they haven’t migrated that much. And they definitely haven't swapped positions. There are important discussions of planetary formation in our own and other Solar Systems. Planetary migration is often key to explain objects like hot Jupiters, giant planets found closer to their star than Mercury is to the Sun.
The observations were performed almost a decade ago but researchers were lacking an extensive spectral analysis of hydrogen sulfide. When that became available a few years ago, the team went back to the data to search for these signatures. It’s a testament to the good quality data collected that this was possible.
The team is now looking a bit further out at Neptune to see if they can spot the same signature there as well. “For Neptune, there’s more overlying haze and we are not sure. It’s likely to be there but if it’s there, it’s even harder to see,” added Professor Irwin.
If you truly want to know what Uranus smells like, be aware that hydrogen sulfide only smells of rotten eggs at concentrations of about 3-5 parts per million. Above 30, it actually smells sweet although it has been described as sickeningly sweet and at that dosage causes fatigue, loss of appetite, and dizziness.