I say if it's something you want, then go for it. For me, a she shed would not be simple and practical, living in central Maine and all. Heating it in the winter, cooling it in the summer, bathroom, electric to it, cleaning it, getting to it over ice and snow, not to mention shoveling a path to it when it snows, I will pass on all of these. Living in an area where it is warm would make much more sense to have one in MHO. I agree with mmunchkins, my sewing studio is upstairs and I feel isolated from DH at times, so being in an entirely different building would only emphasize that feeling in me. I heard the term "Lady lair" on HGTV (ladies version of a man cave) and I liked that name, I refer to my quilting studio as my lady lair.
I enjoy tiny house shows on Youtube and HGTV, and something can envision one of those as an area for quilting ie she shed, all the creative storage, bathroom and kitchentte in place, plenty of space to showcase your work, plenty of room for all the quilt related stations ie: cutting, ironing ect.... room to lay it out, design, and the list can go on...
I hope you follow your dream and it is everything you want it to be and that you get many years to enjoy it, if you decide to move forward, I hope you post pics so we can see your creative space.