I don't believe a map marker is necessary for "Severn Manor" in the Dragonborn DLC. Once you expose the bad guy; it's your place any way as a reward. The Manor is the last house on the left side of town. No biggie! What would be nice is upgrade that dump into a nice bright and welcoming home inside, with lots of the lastest and greastest of everything you could have.
Let's face it! It's your home on an otherwise depressing; dreary, dismal, gloomy, sad, dreary, cheerless,stink-hole of an island. Why not have the best of luxeries while being there to keep not only your treasures that you find; but a place to pick you and your companions (if any) up. Sort of a nice place to rest and recoop after a long mission. Just a suggestion. Have fun.