I thought of this while using cargo refits to haul iron ore in one direction and steel in another direction with NARS 2. I have to use the "refit to" order in the depot. For example, the hoppers start off refitted to iron ore. Orders are go to A, load iron ore, go to B, unload iron ore, go to depot, refit to steel, go to B, load steel, go to C, unload steel, go to depot and refit to iron ore.
This gave me an idea how we can have functional, useful Helper engines in the game.
Here goes: For a Helper/Banker/Pusher engine, have one cargo/livery type refit be invisible, length 1/8, 1 hp, 1 te, and $1 running cost. The other refit is the normal locomotive. Alternately, leave the running cost alone, as this would represent the helper running "light" back down the grade, waiting, etc.
So, a train on a mountain route has a Helper 'permanently' attached (until you remove it.) You start out with the helper refitted to "not there." At the bottom of the steep grade is a depot. The train goes into the depot, refits to the visible & working helper, then tackles the grade. At the top of the grade (or at the bottom of the other side of the mountain, or the end of the mountainous division) the train hits the depot again, and 'disappears' the helper.
In the game, the player would see trains entering the depots, then emerging with the helper engine on the rear (or front, if you prefer, but I hate when I yank a drawbar in the middle of a grade.) You could even have two helpers- one each on front and back, or two on the rear. Then after the train climbs the grade, it hits a depot and "cuts off" the helper(s).
For us realism junkies, if the train was dropping the helper at the top of the grade, we would have to buy a second helper. This one would run invisible up the hill, then refit to visible and run "light" back down to the depot at the bottom of the grade.

So: Thoughts? Would this even work? If so, would it add enough to gameplay to make it worthwhile?