MoPath

# select curve, duplicated objects in group named "duper"
from pymel.core import *
import maya.cmds as cmds
def grpr(name):
    g = ls(name)
    if g:
        delete(g)
    g = group(n=name,em=1)
    return g
pathObj = ls("duper")
# Main Attributes
startFrame = 1
speed = 1
objSpacing = 4
fadingScale = .05
sl = selected()
newGrp = grpr("DuperGrper")
toSelect = []
for s in sl:
    offsetBy = 0
    pathLen = arclen(s)
    endFrame = pathLen * speed
    offsetAmnt = objSpacing * speed
    objAmnt = int((pathLen/offsetAmnt)* speed)
    for d in range(0,objAmnt):
        dup = duplicate(pathObj)
        parent(dup[0], newGrp)
        scaleStart = startFrame+offsetBy
        scaleEnd = endFrame+offsetBy
        keyOffseter = startFrame + endFrame * fadingScale

        moPath = pathAnimation(dup, c = s ,startTimeU = scaleStart, endTimeU = scaleEnd, follow=1, fm=1,fa="x")

        # Fading keys
        setKeyframe(dup[0]+".scale", t = startFrame+offsetBy, v = 0.1)
        setKeyframe(dup[0]+".scale", t = startFrame+offsetBy+keyOffseter, v=1)
        setKeyframe(dup[0]+".scale", t = endFrame+offsetBy-keyOffseter, v=1)
        setKeyframe(dup[0]+".scale", t = endFrame+offsetBy, v=.1)

        animCrv = listConnections(moPath)[0]


        keyTangent(animCrv, itt = "linear", ott = "linear")

        #keyMiddle = ((startFrame+offsetBy) + (endFrame+offsetBy)) *.5
        #setKeyframe(animCrv, t = keyMiddle, v = 0.5, itt="slow", ott="slow")

        sk = selectKey(animCrv)
        dk = selectKey(dup, add=1)
        setInfinity( poi = "cycle", pri = "cycle")

        offsetBy += offsetAmnt