The Chase was the first story to have a future companion playing a different part and of course Peter Pruves would play Steven later on. The Chase was supposed to be the template for the third theater movie and much of the plot was redone in The Dalek Masterplan.
Yeah I've heard that. Kind of a shame they never got to make it, because a big budget, color version of The Chase probably would have been awesome to see.
It certainly would have had more potential for fun than the two dreary Dalek movies they did make (even though I'm sure they still would have found a way to over-simplify and dumb things down).