Need to?
No. We can literally continue spamming Fire IV with Umbral Hearts (If we even bother to cast anything in UI phase other than maybe a Foul or Thunder)
Could do?
Sure. It shouldn't be too difficult to design something that doesn't look like butt.
Really it depends on what you mean by "Tracking"
Personally, I don't actually give a damn about what the gauge says about AF/UI stacks, or the Enochian timer.
Since they aren't important.
Once you hit level 40 you basically don't really spend much time outside 3 stacks of AF/UI. Since your ST rotation revolves around B3/F3 which instantly swaps over and generates 3 stacks. It's merely AoE rotations where you Transpose after Flare (Though, why Ice spells still cost MP I have no idea... If they didn't then you'd B3 after Flare)
Enochian... Well... I'm hardly going to let it drop now am I? Since not only is it directly tied to AF/UI uptime, but also a prerequisite for using F4/B4... Maybe at best, I'll hold on to a Polyglot stack for 20+ seconds to time it so I can double Foul within a burst window.
Even Umbral Hearts you don't really "Track" since you just do your normal rotation but part of it is cheaper.
The same thing would be the case for Astral/Penumbral Hearts. You really wouldn't care, because if they were being made a prerequisite to cast a stronger spell (Such as Burst) then your skill would activate regardless of your tracking (And, potencies permitting, it wouldn't necessarily be advantageous to cast additional Heart generators than you would within your normal rotation)
But really...
We could do with something that can help shake up the rather stale rotation that is looking to be forever 313 during AF and Thunder > B4 (> Foul) during UI.
Like even with your suggested Burst skill, it's still a matter of just doing your rotation but you weave an oGCD Burst after your 3rd F4, while it's still a 313.
It's why I mentioned potentially changing Umbral Hearts so its something a little more interactive than "Just do what you were going to do anyway" and allowing Astral Hearts to be something that shakes up the 313 AF phase.
Allowing Umbral and Penumbral Hearts to be dedicated to making UI phase not total garbage - With the caveat that these are temporary and gained over possibly multiple rotations (I.e. If Thunder generated a Penumbral Heart, that's 1 stack per rotation, outside movement using TC procs)
Like, if I was to spitball something... Maybe like, having Fire IV generate Astral Hearts which then power up your Fire I turning it into (Placholder Names) Fira, which does more potency and guarantees a Firestarter proc which lets you use an upgraded Fire III (Called... Lets say, Firaga) and then casting that allows you to spend your final Heart on Comet.
So your AF phase is more like Fire IV > Fire IV > Fire IV > Fira > Firaga > Comet.
Maybe there will also be a cooldown that allows you to instantly get 3 stacks of Astral Hearts. So you can set up for a burst window by just doing Fire IV's during AF and then during the burst window you Fira > Firaga > Comet > Refresh Hearts > Fira > Firaga > Comet.
You know... Trying to mix up the rotation somewhat by making it sometimes advantageous to deviate from 313 to manipulate your resources.
Maybe there could be something similar during UI, where you spend UH's on Blizzara, Blizzaga and a not trash Freeze and then follow up with a Burst if you have one ready?
Again "Need". No. We don't "Need" anything new. Technically.
But Comet is cool. It's also something that won't just be "Fire V" or "Fire VI" or "Fire VII"