I've been messing around with using only the first hit of dancing blade from short hop as a combo starter. My main experience with fighting games is in Street Fighter/Tekken, so sorry if I get some of the Smash slang incorrect.
Short hopping into the first hit of dancing blade seems to set up combos once you have gotten some percentage on the other player. The first swing perfectly sets up nair and up air to auto-cancel upon hitting the ground due to it only being out for a small number of frames. Depending on the other character/percentage/your percentage/move freshness/vectoring/etc you can follow up short hop side b, nair into tilts, jabs, full dancing blade and possibly smashes. This isn't as good as short hop double fair or anything, but it could open up more possibilities for Marth. You can also use the first hit of dancing blade to meet an opponent in the air and link it into fair/up air depending on their positioning.
I haven't fully confirmed any of this, but I thought I would throw it out there so the better players can try and come up with something using it. Here are a couple of quick gifs against a level 9 Mario. It's not the best way to show off the possibilities, but it was a quick way to get some footage. Unfortunately I'm blocked from linking the webm versions because I'm new!
Short hop side b, nair, up tilt:
Short hop side b, nair, forward smash:
You can see I'm a bit slow with the forward smash here, it might have been possible to have air dodge out of it. I tested against a level 9 ai in training, which usually dodges or jumps out of this if I mistime it. I think it's possible to land a smash using this under the right conditions, but I didn't capture a good example of it.