OK, sorry for the redudant question, found the reference to another Post describing the keyframed speed Suggestion which is has already been taken into account.
Just as reference, I currently use SlomoVideo to do my slowmotions. it builds well on ubuntu, on windows I have not been able to build the project, so I have started scanning through the code a bit and was thinking of possibly guiding my efforts towards incorporating a variant of it into shotcut if possible.