Putting $LOT in a TX and adding some keyframes makes funny stuff, but I cannot see the point.
I'd say segement is the part of a curve between two keyframes, but I cannot enter values to shape the curve and those variables to read something, can I?
There's also $IV and $OV which gives you the left and right keyframe values respectively. Combined with $LT (local time), $LIT and $LOT, one can create their own custom segment interpolations. There's also $IM/$OM for slopes, and $IA, $OA for accelerations.
Is it possible to get the channel variable from another channel? A function or something whose arguments would look like chanvar("../../geo1/tx", IT)? (i.e. get beginningtime of the current segment from that channel)