That particular example seems rather ill thought out and poorly defined. Why the Wellington Cup carnival is specifically mentioned doesn't make sense. SI based horses during the period which tackle other NI races will be excluded? The description of the primary requirement "located at a SI training facility from midnight 31 December" ... what does that mean? Presumably the horse can't go for a spell or therapy during that time? Or are SI spelling/therapy facilities, training facilities? Is the beach a training facility?
If you go by the definition of that in the rules a lot of SI trained horses will be ruled out. The likes of the Parsons' stable, a big part of the Pitman stable etc. spring to mind.
Training Facility means any place at which horses are actively trained or worked and:
(a) which is owned, leased or occupied by a Club;
(b) in respect of which a Club has any right or ability to access; or
(c) which is reasonably believed by NZTR or a Tribunal to be in some way used by a Club
Why December 31? You'd think for this to possibly advantage SI based horses it should be for the season or thereabouts. Otherwise, a horse can have a spring campaign from a NI base perhaps culminating cup week here, then a spell and back in work for the target race from December 31.
Then, as you say, NZTR being the sole judge raises the question of whether the big players will be able to make an acceptable case for eligibility whereas the small players may not.