The only major issue I see is the use of 2.4GHz. That band is crowded in many areas - in my house wifi and Bluetooth are pretty much unusuable unless I switch to 5GHz. Range is also a major issue.
We have tested the range and have gotten 84 meters. That was under more ideal conditions so we generally say the range is 50-100 meters. Under bad conditions, where there are a lot of walls ect a 30 meter range is more realistic. We are easily able to get to every corner in a large house. As for the band being crowded BLE has very good frequency agility.

This image shows the available BLE bands vs zigbee and wifi channels 1, 6, and 11. WiFi in North America is only allowed to operate up to channel 11 leaving a fairly wide gap for the 2Mhz BLE channels. The other thing is that our BLE connections are very short so the total airtime taken is minimal. All in all we have had no problems but it is obviously not 100% immune.
For the ISM bands the primary problem is that there is not as much choice for very low power devices. I think a future version using the ISM band is definitely a good choice.