Plasma is a bit hotter than your gas fireplace flame. Common lighter flame is at about 600 deg C and while it's possible to create plasma which is nearly ambient temperature in controlled environments it's generally tens of thousands of degrees (plasma arc welding for example) up to tens or hunderds of million degrees celsius (inside fusion generator).
That's mostly why fusion energy is so difficult problem to solve in the first place as there's no materials which could withstand the heat. So, no, it wouldn't be useful as a fireplace. It would of course radiate heat, but it would also light your (and your neighbours) house on fire, so not that useful.