Can I ask what you have in mind to make mitigation seem more interesting or impactful? More active mitigation? Choice mitigation (maybe some shared resources so you have to be more picky about what you use, but also each can be a bit more powerful as a result)? Should it still be just as front-loaded as now, where as long as you have all your CDs ready you can take on an army, and when you don't you take on an army of mice? Or should it be pulled back a bit? Should diving into the fray have more advantages than just more mitigation output and the few sustain tools like Bloodbath Overpowers or Blood Price? Should offensive, defensive, and utility ever feed from any sort of common resource so that you'd have to pick between those too?
I feel like there's some good points that come out of the system we have now, even if far from seemingly perfect. Front-loaded mitigation toolkits give us a fairly large capacity range or periodic variance around which to pace our runs, which brings out the feeling of the tank as a dungeon leader, the pace-maker, and necessitating variance in that pace. The simple CDs (no charge, just refresh, with any time left unused after recharge going to waste) gives near-obligatory interactions in healer-tank trade-offs for focused output. Their length makes it timeable against very certain attacks in a given fight. Their cooldowns incentivize strategies for non-forced tank swaps, pre-popping CDs to catch the next applicable even if the first's duration would partly go to waste, etc. There's quite a few good things to be said about it, on the whole. Which or, moreover, what could be better? Which are worth throwing out for that something better?
There's also the balance of mitigation (both anti-burst and anti-sustain) and damage-dealing (both burst and sustain). I'd ideally like both to feel impactful, but I don't want to see the simultaneous capabilities of tanks so overwhelm those of DPS that it'd just make sense to go mostly tanks? An extra or two in an 8-man—I'd like to see use for such variance, if merely optional, just as with healers. But just as much as I don't want tanks to feel unimpactful in their mitigation or like wet noodles in their damage-dealing, I don't want to see non-tanks as a burden.