Whilst there have been no complaints to date, I don’t think that is grounds to remove it.
The stated intent was that this clause would be to deter potential confusion, I had understood it to be a means to resolve potential issues. If the clause is removed, an alternative process/channel would need to be clearly identified to allow a complaint to be properly and fairly dealt with.
If the generic ‘isp.nz’ were registered and the registrant were to delegate ‘vodafone.isp.nz’ and ‘spark.isp.nz’ to random third parties and if those 3rd parties behaved in a manner detrimental to the real Vodafone and Spark, I think the real entities would have cause for concern. I think it is unclear how those concerns would be handled.