One thing you could do is simply have it take effect (at no cost) only when you are perfectly in front of the enemy and have that enemy targeted. This would be automatic if you had threat, but you could potentially play with the mechanic by allowing the ELM to parry attacks not aimed at you. ELM would thereby become more supportive, moving into tank position for AAs and dodging back out before cleaves. Just a thought.
So does each reversal (fire-->water or ice-->fire, etc.) constitute a stack, or each full rotation of elements? In either case, if the Arcane Cycle is basically foe-only, there really is no free-floating concept to it to speak of (not to say that you implied there was; it just tends to seem a level less significant to the class when the concept is simply a result of action). Instead, each attunement debuff simply grants a stack of charge, <Arcane Cycle>, whenever an opposite element is used, and certain abilities then consume that stack.
Basically, it makes me wish there was a native version of the Cycles as well, such as an attunement buff on the ELM itself, that required strategy to sync up with certain future wants for the elemental uses. This complexity would also be aided by having more than just Burst and Doublecast to spread about mobs, syncing up their debuff elements differently.
In a lot of dungeons, mobs don't last 18 seconds. You may want to drop the original time down to 9, or have the attunement effect take place after a certain minimum amount of damage has occured, where DoT crits could accelerate the readying of the debuff, and it on average goes off about 9 seconds with no crits and faster with them. "Cycle Through" could probably use a better name as long as the speed of elemental wheel rotations is its only major element effected.
Even as a support, RDM doesn't have to have lackluster abilities. Try to imagine scenarios that really stick out to you and make you want to play the job. Who all does it pair with, when and why, and how does it affect the linked party members' rotations? If it doesn't affect their gameplay at all (not that I recommend that a paired class should have to outright renegotiate its rotations to better benefit from RDM), such as a general dps increase or a minor benefit that doesn't allow for any extra action or opportunity (e.g. a skill speed increase that doesn't allow for an extra ability per shorter rotation), it will be that much less interesting.
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To be honest, I still think ELM doesn't really have a place as a class, especially as *the* rapier class. I'd much rather see Fencer used with the Fencer weapons, and for its elemental abilities to seem only either coincidental or stylistically-matching to an otherwise physical repertoire. I think that also brings more of the unique spellblade style of RDM than if starting from a caster class that happens to carry a sword and uses a couple sword finishers. I'd recommend reading MartaDemireux's take on the RDM. It's not exactly what I'm recommending by any means, but it will give a better example than I can illustrate in writing here.