In some cases, it could be useful to be able to define for some higher-order type extension methods with additional type parameters
Yes, and hopefully that will come at some point. To do this right we need to support multiple type parameter lists on methods, which is non-trivial. Before we get there I’d rather not do something
temporary (like merging parameter lists) since it would likely make it harder to do the right thing later.
For the moment, we have made sure that Tasty supports multiple type parameter lists. So we can upgrade later without changing the format.