Well, the suggestion wasn't supposed to really impact the AoE rotation. More so to add in a DoT in a way would allow for some extra damage utility, such as increasing damage while movement is required and having a form of passive Mana generation to play with that can aid with increasing the rate at which melee combo's are generated without simply slapping bonus generation onto existing skills.
Adding in more AoE's for the rotation... Is a much different proposition. One that I haven't been able to make a particularly satisfying rendition for. Only thing I've been able to come up with is replacing Enhanced Scatter (Possibly with a Scatter II) with an Impactful II buff that allows the use of an Impact II which is an AoE form of Impact with higher damage and Mana generation than Scatter (II).
A concern was with button space though... However, I suppose that Jolt and Scatter could simply be replaced by Impact and Impact II respectively given that I don't believe there's any reason you'd want to use the base versions over the Impact procs.
A fun little side note is that it would mean that RDM would be one step closer to being a Flower Mage with more flowery Impact casts ;D
I guess because of two reasons:
1) Tying AoE damage behind the ST melee combo is not particularly fun design (It's a similar situation to WAR with their AoE Beast Gauge spenders, whom can only generate Beast Gauge with ST skills so can only use Overpower in AoE situations outside of using Inner Release to bypass Beast Gauge costs)
2) Allowing use of Verholy/Verflare after say, a (New) Moulinet combo would be awkward as they'd imbalance Mana while RDM AoE rotation builds Mana relatively equally given it mostly spams Scatter as opposed to alternating between Black and White AoE skills akin to the ST rotation.
With a possible third reason being to try and signify that BLM and WHM are more potent in their respective schools of magic compared to RDM that utilizes both. So that the RDM versions of these ancient magicks are only powerful enough to harm a single target.