Skelton has raised the bar in spectacular fashion this season. He is so far clear of Henderson and Nicholls that they should be embarrassed. It is difficult to see either being Champion Trainer again.
If Skelton maintains this standard, I doubt Mullins can win the title again either. He would need to run horses regularly throughout the British season and that is not likely to happen, especially with Elliott having undergone something of a revival this season.
Perhaps Mullins won his two British titles in a short window of opportunity, in between Nicholls and Henderson falling away and before Skelton was in a position to take over.