A while back I was given a Dracaena (I'm not sure of the species, but its leaves are narrow and about 12 x 0.5 cm) that was in pretty poor shape (it was grown to around 1.3 m high and had three branches) but I took a cutting, placed it in a jar and roots have emerged. The longest roots are now around 7 cm long. I really quite like how it looks, and it's putting on good leaf growth as well as the roots. Could this be a long term setting for the Dracaena? The only potential issue I see so far is a wet stem up to about 1cm of the water line, I'm unsure whether this may cause issues in a few weeks/months.
You can keep it in water long term, but only the roots the stem should be kept dry. What you have is a very very basic hydroponic set-up. You will need to change the water often to keep fresh water that is full of oxygen. You will want to use a heat mat to keep the temp of the water around 20°c (70°f). You do not want the water to get too hot, because warm water holds less oxygen, but you do not want it to be cold, because this a tropical plant. You will need to add nutrients. It is important that you use nutrients developed for hydroponic crops. You also want to make sure your container is not see through. A see through container will get algae build-up once you start adding those nutrients. This becomes a much bigger project than it would be if it were planted in soil.