The challenge/goal is to have an entry level sequence that can be flown by a very broad range of pilots with a broad range of planes (including trainers).
We did exactly this for a "fun Fly" type event at our club. We flew the Sportsman sequence before our primer, everyone, regardless of current class had to fly sportsman... but if you were an active pattern pilot you had to fly a 40 sized trainer. The current sportsman sequence is definitely flyable with a trainer and it was a good event for the club and reinforced what we have been saying all along that you can win sportsman with whatever you are most comfortable flying... even if it is a 40 sized trainer.