Couple random ideas to consider:

Use SN accounts as Nostr accounts

• SN could provide one click experience for creating Nostr account (it would automatically populate NIP-05 and also lightning address) - private key could be shown only client side, but maybe also store password encrypted backup back to SN?
• each SN user could get public and private key (that will be needed for decentralization anyway - initially as part of migration SN could store the private keys - and maybe allow users to migrate to their own private key?)

Use Nostr accounts as SN accounts

• if nostr user has LN address associated with their profile, they could have streamlined account creation in SN?

Smooth out experience between SN and Nostr clients

• SN should have much better profile page, that could include both SN posts and things and also automatically show all Nostr related things. Like if I want to see some known person I would go to SN and would see summary of all their SN posts, their Nostr posts, etc.
• SN could provide a button to "share on nostr" when your SN account has nostr account associated?
• Nostr clients could show better previews of SN posts and maybe allow direct tipping to the users

Use nostr for posts/comments

• this one is the trickies and most questionable, but after the steps mentioned above are done, SN could actually use nostr for handling of comment threads per posts and ultimately also handling of posts (there would need to be a way to separate the "I'm posting random comment about my life" and "here's great news / article link")