Only women hostel or budget hotel.
Women has become frequent and independent travellers these days and would have travelled even more if have felt themsleves secure. I myself travel a lot and know that hotels specialized on women are a rarity and quite expensive one.
As a an business person I see the number of tangible advantages which will have positive impact on the existing business model: women are more clean, accurate and orginized at the same time they less agressive, violent, and drink less on average hence the hostel will require less spending on cleaning and maintenance annually, less damages on furniture and equipment. One can object that the demand is significantly smaller than in case of men but at the same time they are easier to target and as I said such hotels can be counted with by single numbers.
I am thinking about european capitals like berlin / madrid / amsterdam / barcelona and although the business model for the hostel is quite simple itself I am still on the early stages as need some partners for inspiration and motivation.