I designed the rules around which the Uniregistry Marketplace operated, and the Rubik's Cube of "how to get a business model to mesh with ICANN domain registration rules and financial regulations" is enough to drive anyone bananas. So, I'll just throw out a few things you might want to think about. Some of the "things to think about" apply to both models.
1. Marketplace takes ownership model:
you send it to SuperDomain by either directly transferring ownership
(a)
Liability. Unlike commodity goods, a domain name can be a liability bomb waiting to go off. It is very brave to accept the potential liability of becoming the owner of whatever domain name someone chooses to list in the marketplace. People list all sorts of trademark infringing domain names for sale, as gets pointed out on this forum all of the time. Now, of course, SuperDomain can vet each one, but that's going to require some overhead to make sure (to at least some degree of comfort) that someone is not bulk-listing a portfolio of dicey names.
There are some ways of managing that, but even if SuperDomain assumes some sort of custodial role, 15 USC 1125(d) doesn't merely refer to registration of cybersquatted domains, and the "trafficking" part of "registers, traffics in, or uses" has never really gotten a lot of attention <
https://www.law.cornell.edu/uscode/text/15/1125>.
(b)
Trust. It will require a pretty high level of trust to have people hand over ownership of their domain names to SuperDomain. Grizzled veteran domain investors who have endured decades of scandalous behavior by registrars, registries, marketplaces and other service providers do not have a deep well of trust, and even the best get burned from time to time.
(c)
Renewals. Anyone will tell you that domain investing is largely a waiting game. Domains can sit on the shelf for a long time. Is SuperDomain paying for the renewals while the NFT is floating around in the wild? I transfer the domain name to you in January and you issue me an NFT. The domain name expires in March. What happens next? I assume SuperDomain is not paying to renew everyone else's domain names, but how are renewals going to work? This isn't a monkey jpeg sitting on a server somewhere for as long as the server lasts. A domain name needs periodic renewals and can't be renewed for more than ten years chunks.
(d)
UDRP/Litigation Transfers. The domain name I transferred to SuperDomain is stolen, infringes a trademark, belongs to a company in bankruptcy... whatever. A court or UDRP panel orders the registrar to transfer the domain name to someone else. The registrar does so, and the new owner moves the domain name to their preferred registrar. The NFT, meanwhile, has lived a happy life and has been sold five times. I imagine the current owner of the NFT is just left holding the bag, since SuperDomain no longer has the domain name to redeem the NFT. How is that going to work?
(e)
What is the domain name doing? From the time the domain name is listed for sale to the time that someone redeems the NFT with SuperDomain to obtain transfer of the domain name, what is it doing? Is it resolving to SuperDomain? Can I use the domain name for some website and email while it is listed for sale, or is it effectively unusable from the time the NFT is issued to the time it is redeemed? How that question is answered then branches out into a couple of other potential issues.
2. Marketplace as Registrar model:
transferring it to SuperDomain registrar while maintaining ownership
This is, in general, a little easier to administer. A middle ground is to have SuperDomain be a reseller, depending on the extent of management control the registrar provides its resellers.
The "marketplace is the registrar" model is still going to have some of the issues above, but the workarounds might differ. You also have to deal with the fact that transferring a domain name from one entity to another has to comply with the ICANN Transfer Policy. There are some workarounds for that, such as establishing the registrar as the agent of the registrant for the purpose of carrying out or denying transfers under the rules for the marketplace.
But, at all times,
someone has to be the registrant of the domain name, and that someone will have been required to provide the required identification data elements and to have confirmed them to at least the level required by the ICANN RAA. If I'm the owner who listed the domain name and I've sold the NFT, I can go on my merry way with my proceeds, but if nobody shows back up to redeem that NFT with SuperDomain, am I going to remain the registrant of the domain name? I'm surely not paying the renewals, and I doubt SuperDomain is paying them. But who is SuperDomain putting in, for example, the monthly registration data escrow deposit as the registrant of the domain name? I already sold it as far as I'm concerned, but if that NFT is traded anonymously 10 times in the ensuing months without anyone showing back up to de-list it, then how do you envision that I quit being the registrant of the domain name I've already "sold"?