If you really want to do this and be successful, you've got to consider price, like everyone else has been saying, but also marketing. I think Dyson was very smart about that, and I remember wanting one when they started to appear. I didn't know anything about vacuums, and most people don't. I had thought bagless was a great idea, and I believed from the commercials that they were great vacuums (not realizing the first vacuums were bagless). When I wanted a Dyson (because of the marketing), my parents still went with the latest Kenmore bagged canister. But now that I know more about Dyson and don't want one, my parents went with a Dyson, and I hate it. They wanted the Dyson simply because it was bagless, and that was probably the best brand that they were familiar with offered in a big box store (because of all the commercials). They did not research vacuums or try them out.
I think you would have to create a vacuum that is priced lower than the Dyson. I think the Shark commercials are good at showing that they offer the same vacuum (if not better) at a much lower cost.
You would also have to create a design that stands out, something neo-retro.
You would have to offer a new gimmick. Perhaps a chamber system that filters out large items like toys that might accidentally be vacuumed up by a careless person which could be retrieved later from a clear compartment within the vacuum. (we can all agree that people are careless and hard on vacuums) Or perhaps a special trash can adaptor that hooks up to a bagless canister that transfers the contents from the canister into the trash without any of it getting into the air (essentially a 2nd vacuum to empty the vacuum!). Or perhaps you could invent a vacuum that incinerates its contents, meaning a vacuum you'd rarely have to empty.
You also might want to research what people are looking for in a vacuum. Not people like us, but people who don't really know anything about vacuums.
And you'll want an unforgettable commercial (that is probably subtley sexy to give you an edge). I think that's how most people are educated about vacuums, and Dyson did a great job teaching people to believe they were making improvements and a better vacuum...when in reality, I'd say they created a 'different' vacuum. Bagless was not new, the cyclone wasn't new, and the ball was a gimmick. But they sold it on TV as new and revolutionary, and better than the average vacuum. Over the last 5 years, I think I've seen more Dyson commercials than any other, and they've been consistent. And now there's a Dyson at home. I wonder how long it will last.
**I am not attacking Dyson, but I don't think they are the best vacuums. They were however, very smart with marketing and advertising.