I like this quick summary of flow, something I wish to be able to dedicate hours of my time to.
I believe that flow in itself can be a little deceiving unless carefully planned out. Feeling flow without challenging oneself enough or not trying to stretch in terms of meaningfulness seem dull.
Reaching flow through carefully mapped out meaningful work seem very attractive to me though. So by making flow in itself a motivational reward to reach, we may progress as a species.
Remembering that it must fit the individual is key. This is most likely where we must start to reach flow.
Remembering the importance of meaningfulness is probably best carried out secondly.
Lastly, finding the right balance of challenge will totally be an ongoing challenge.