This idea was suggested a while ago on the Red Eclipse forum at freegamedev.net. I'm also discussing it there, but I realised this could also apply to Sauerbraten.
Here's the idea: a variable called "vcurb" or "vslide" that could be used like "vrotate" and others. This variable would scale the slipperiness of the surface a player is standing on, like Red Eclipse's "floorcurb" var, but applying only to certain surfaces instead of the whole map. (note that "slipperiness" in this case only applies to momentum, not to how easy sloped surfaces are to climb or slide down.)
The main discussion on whether I should pursue this for Red Eclipse is in the link above. The purpose of this forum topic is mainly to discuss whether the Sauer community would like this to be included in Sauerbraten as well.