Random access write performance (followed closely by random access read performance) is the main bottleneck for Roon–or at least, it’s the main culprit in the worst experiences.
Whenever you get long pauses–during editing, metadata updates, imports, etc, we are almost always writing out a ton of records to the database, updating indices, etc. This is the reason why SSD is practically a requirement for Roon.
Most browsing/searching is served up out of RAM, so a faster disk won’t make focus or search faster. It will just make the RAM-based data structures load up a little bit faster at startup (who cares?).
Looking forward: We’re in the process of making new search indices–as search gets painful with large libraries. A lot of the core library/database management stuff has been re-organized to cut disk accesses by about 50% and reduce write amplification during certain pathological index-update patterns by over 90%.
I suspect that the performance work we’re doing will make a bigger difference than incremental hardware improvements.