I understand why they're doing this because of the new laws with them having to report to HMRC etc.
The issue and concern is, What IF eBay was to be compromised and this data leaked...NI is pretty important information and a NI number leak can lead to all sorts of issues for its users.
Hackers would have a field day with NI numbers.
Was this even taken into consideration when been implemented?
Obviously the government/HMRC wouldn't care...they only care about getting their tax.
Have to question these things!