We keep a list of domain names as custom asset type in Syncro. We use this for ticketing and various billing counts. I have no option to sync the domain names from there to Hudu other than bring them in as a separate asset layout. This does not help as I cannot get expiration and other details. Please consider making Websites able to receive synced assets from the PSA and also as the other posts have mentioned, separate the concept of a domain from a web site. All websites relate to a domain, not all domains are web site. Maybe make a new domain asset type, allow syncing and then when they are added you can specify with a checkbox that this domain is a web site. Also to be totally clear, some domains have multiple web site.
example.com is a domain
www.example.com is a web site
hudu.example.com is also a web site
All these web sites are related back to the same domain.
I will stop now so as not to get too distracted.