Purely as a point of information, I think its worth remembering that 32 bit ASN cannot be used in currently specified BGP4 in communities, because its a 32 bit field defined as two 16 bit halves. I believe there is work afoot in IETF to fix this. I don't have concrete details.
Therefore there *is* a quality in 16 bit ASN which may be divorced from its association with specific V4 or V6 resources and which makes it a desirable thing, in itself, for some people: If you are in the business of doing TE in BGP with communities, you can't do it with 32 bit ASN. You have to use other mechanisms.
On that basis, Should you permit transfers of ASN, you might wish to permit transfers of ASN independently of any associated routable IP address space: people who already have space but need a 16 bit ASN may wish to acquire one.
I'm not an asset holder in the RIPE region, and I am staff at another RIR, so I stress this is purely informational. I'm not trying to directly advocate for or against ASN transfers.
-George