Not sure this is possible or not, but going to use PLEX on the shield as a comparison.
Long press on the remote triggers a run up to full speed scrolling… it’ll do a few incremental speed changes then go flat out.
One of the nice features on PLEX on the Shield, is the long press seems to go to max on long press after a short delay causing a buttery smooth scroll effect rather than Kodi’s somewhat clunky steps.
Not sure if possible but anyone who has used the 2 systems will know what I mean. Hope i explained it properly!