Ronja operates in visible light band which was allocated by the Sun about 5 billion years ago and will occupy the band for another 5 billion years. The visible band is outside of governmental regulation (except for eye safety) in most countries and it can be expected that it will never be regulated, as it's used for mundane activitites like lighting.
Links operating in free radio bands are potentially susceptible to future interference by newly built stations of other users. No such problem exists with Ronja because the beam is very narrow (4 mrad, a 4m diameter circle 1km away). A government can potentially decide to close down a free band and start selling licences. This is unlikely to happen with the visible band.
Links operating in licensed bands are subject to licence payments. Even in these bands, a government can decide to close or narrow down a band and change the purpose of it's usage. Such a decision is going to render an existing device unusable because generally it's difficult to retune a radio device to a different frequency.
The amount of background interference in free bands can vary too. For 2.45GHz bands this background is created by microwave ovens, bluetooth devices and other devices using 2.45GHz (for example wireless cameras). No such problem exists in visible band. The background interference is generated solely by the Sun, which is the same for billions of years and will stay the same for as long. The availability of Ronja is bounded by occurence of fogs, for this to change a substantial climatic change would have to occur.
These properties of Ronja can be summarized as that a Ronja link is going to serve in undiminished way into practically unlimited future, without being influenced by any human activity. Ronja will not require any future reinvestments except maintenance costs (repainting the metal, which can be done together with other metallic parts of the building, and replacing the 1$ LED every 5 or 10 years).