I figured you wouldn't have to lose your housecarl because they will just be stationed and always found in the Jarl's area from then on.
Now I'm not expecting a return on my investment or any projected profits. Even though that would be cool. Especially if the price was adjusted depending on when you chose to sell it. Basically like a simulated real estate market. I would just like to sell my old homes back to the city even if I take a hit gold-wise. It would be cool if they actually compensated you for having the house entirely furnished though. Maybe even account for whatever items or valuables you have in there. Perhaps what they could do is set all your items in a storage unit somewhere in the Jarl's palace right after selling the home.
What would you guys think of having the ability to sell your formerly used homes back to the city? It would be completely optional of course.