A cloud TSS is not affected by a potential exchange and the associated financial and time expenditure. The implementation as well as the certification concerns only the components in the fiscaly cloud, not however the components with the final taxpayer locally. In the worst case, if something should change at the interfaces, a software update is necessary.
With a hardware-only solution, there is a risk that the hardware will have to be updated within these two years. Once a TSS has been fully certified (probably between 2020/2021), the certification is valid for five years, afterwards the TSS has to be recertified. If adaptations are necessary in the meantime, existing hardware TSS must be actualized with an update.