Yes, and most importantly, it would give mermaids a habitat.
Playing a mermaid and not seeing anything underwater is frustrating. There's nothing special to do as a mermaid that you can't do with a sim apart from like 4 interactions that have little real impact anyway.
They sleep by back floating, that is just crazy. At the beginning I found it charming but then, I realised it was the same animation as back floating but with the Zzzz sign. Mermaids should sleep under the sea. And they should have a place to call home. They should feel out of place living as normal Sims and they should be able to travel to their secret mermaid lot deep in the sea.
And then, as you say, if they like a SIM they can show them their "world".
