I've been looking through the speedruns and realise that a nightmare category is needed for a harder challenge, every other skylanders game has one. For linear you have to do the levels the way they were designed, I would like to be competitive but I don't have the money to buy skylanders for the advanced tech.
Nightmare could possibly be added to the category extension board, the main board already has two variables so it would be very cluttered. Your description of a "linear" category is essentially glitchless, which does not really have enough interest to warrant its creation at the moment. Possibly later, if more people become interested in it.
Nightmare would not be very special for runs with imaginators as you just one hit everything to begin with.
It has been decided that we need to have a consistent and easy to understand method to retime runs of this game without loads. There have been changes in timing methods in the past, but they have never been applied to every run on the board, so timing methods between certain runs vary. To help with