At the moment, in Rhythmyx 6.5.2, there is a 50 character limit on labels in keywords. We are starting to run into that limit in some our uses of keywords to populate dropdowns with options. For example, in a dropdown to allow authors to determine the layout of slots on a home page, we have keyword values with labels such as “Slots 1,3 in left column, Slots 2,4 in right colum” - the final ‘n’ is missing because it would be the 51st character.
I think long labels would be worth the penalty of extra storage space in the database. I would suggest 128 characters would be a sensible maximum.