Hi Felipe
If I was in the need of additional IPv4 space, I would much rather go to a location that is (a) central (b) legitimate (c) verifies that the transferer actually has the rights to the address space and (d) where I can be reasonably assured the sellers abide by RIPE policies.
I assume following recent discussions that those brokers found breaking RIPE policy are now actively being removed, so this list is probably the best I could hope for. And any other listing service would not have the ability that you do to verify that the user has the address space in question registered to them.
I would much rather this service continue to be maintained by the NCC than have to trawl the internet and deal with some of the shadier characters out there. And I don't feel it is a big ask of the NCC, as it falls under the core remit of responsible stewardship of the resources.
And a note on the timing and your perceived utilisation statistics. Just because I have not had a need for it just yet, does not mean I cannot foresee a circumstance in the near future where I will need it. We have only just reached the point of IPv4 runout.
I would also raise concerns that "a full reimplementation would be needed to continue supporting it" - how has it been allowed to be developed in such an unmaintainable manner that this is the only way to continue operating it?
Regards