The problem with the Regenerative Shields is that the numbers pale in comparison to active heals. Doesn't matter how often it ticks, or how much it ticks for when active heals leave it in the dust, and if the active heals don't then there's no reason for those powers to exist. No one is going to rely on passive shield regeneration when you can actively restore a much more protective Covariant in a relatively short amount of time.
The only thing I could see that might make Regenerative Shields enticing would be having active heals scale according to shield type. A bonus to effectiveness versus Regenerative, a penalty on Covariant. Since we are always going to rely on active heals you need to factor them into the proverbial "Healing Shield" in order to make them worth consideration. This might actually make them attractive to ships with naturally high shield modifiers like Science Vessels.
I actually use regenerative shields on my cruiser and like them a lot. Borg/triple cap mk x is nice. Trick is to use them with high shield power of 75 min with power/buffs boosting it to 100+. I believe at 125 you get x4 the regen, on a sci captain you can have like 380 regen on them 380x4 = 1520 shields every 6 seconds.
Emergancy power to shields 3 + Transfershield strength 1-2 + 100 and up shield power will pretty much max your shield resistance and boost your regen. Use them all together and regen shields are extreamly hard to punch though.
If emergancy power to shields 3 regens 3k shield but has 45 sec cooldown thats 66.6 shield restored per sec over time. In 45 sec regening 1520 every 6 you regen 11,400. Once you do the math you see they arent to shabby. I love them vs the borg because even if the borg drain your shields and your boffs are on cooldown you will restore a lot of shielding while they recharge.
With the +35% cap console in my cruiser i have the same amount of shields that my old mkx covarient had before the console came out so they are pretty even in my book and yes i use them in pvp. They could use a reduction in regen time to make them slightly better maybe 4 seconds but if you dropped it to 3 seconds it would be overpowered in my book. 22800 in 45 sec without regen abilities would be a lil nuts.
A faster regeneration cycle has a particular benefit that is not just measurable in total hit points recovered - you spend less time unshielded then any other ship. That makes timing a Tri-Cobalt or Quantum Torpedo spike more difficult.
But the overlal regeneration value over time matters little compared to shield heals. And the Covariants benefit more from these heals then Regeneratives, as you can't "overheal" that easily (and if you don't heal to ful, you are still benefitting from the Covariants weak Regeneration. A regenerative shield at the same hit point value would probably stop regenerating as it is already full.)
A way to address this might be to have all shield heals a mix of instant heal and heal over time.
The instant heal could be increased for Covariants, while their heal over time would be reduced for them, and vice versa for Regenerative Shields.