This is impossible due to two reasons: player skills and overgearing. Exceptional players optimize every gcd and cd they have to reduce the strain on healing, and if you set the bar for minimum healing requirements that high, the contents will be impossible to clear for the large majority of players. As I've mentioned before in an earlier post, the performance gap between good and average players is just too big now. If you make the good players have to constantly heal, the average players will have no chance at all to clear the content. The other reason is self-explanatory. If you have to constantly heal at i270 then you won't be able to clear it at lower ilv. If the content is beatable at i250, the same people who beat the fight at i250 will inevitably have more downtime to weave in dps.
Have you ever watched vids of savage raid speedruns? If you watch them and check their fflogs you'll see the amount of optimization and coordination between healers and tanks is something out of reach for most average players.
