Think part of the problem may be spam or scam coins. Any such venture in this direction has had to low volume and demand to sustain towards any growth. But there is some demand and growth being evident with XCP and NXT assets.
It seems like it. It is surprising there has been no interest in this yet. XCP and NXT do they trading on-chain. ColoredCoins would allow trading on central exchanges with high transaction times. There are likely other potential uses cases.
Think the high transaction times and lower trading fees may become useful at some point. Maybe now just isn't he time. As we are all growing and learning further in these crypto mediums.