Cities like London and HK have long been used pico cell to support to ever growth demand of subscribers. Femto cell was originally introduced as more or less a private cell. The business model may change that femto cell may serve more than just a household.
With the popularity of WiFi, indoor coverage may be better off left for WiFi. Outdoor can still be served by different cellular technologies in the long run. Well! In the long run, GSM might very well disappear for good. LTE will be the dominant technology.