I was unfamiliar with Lenny Rush before the New Years Special episode.
I know he won the one off special - that managed to work the small number of tasks so that he wasn't inconvenienced - but I'm not sure how they could have someone like him, or say the blind Chris McCausland, on for a full series of 10 episodes (so 30-40 tasks)?
They had Chris McCausland on House of Games recently and, points wise, he did well - but, again, in order for that they had to change the format so that there were no visual rounds which meant it was a very 'samey' week with plenty of audio rounds each day. It was fine as a one off, but was one of the poorer weeks in terms of variety of rounds so the show would be worse if they had to 'dumb it down' too often.
And I think the same applies to Taskmaster. I can see how the one off New Year Specials can be tweaked for someone like Lenny Rush, Chris McCausland, Rosie Jones, etc, to participate - but I'm not sure how they'd manage to come up with 30-40 tasks for a full series if they were seriously limited in how physical / visual any of them could be?