I think it will a small buff in most cases.
1. This allows you you split your innervates between multiple targets. Ex Healer dies, you BR and innervate them, then 3 min later use the second innervate on yourself. Which should be nice since BRs are largely what put me into potential mana problems in the first place. This assumes you would oom before 6 more minutes pass and\or boss would live that long. Ex2, as someone said, you could innervate 2 healers giving each a boost to last the fight instead of making one end the fight with 40% mana left while the other is oom
2. If you innervate early and often, you will always get as much mana as now and often get more much more. This assumes first 3m innervate at 2min and then recast when it is available again, rounded up innervate to 15.8k.
Time 2m 5m 8m 11m
3m I 7.9k 15.8k 23.7k 31.6k
6m I 0 15.8k 15.8k 31.6k
3. Since it will be available again so much sooner, people will be less stingy and innervate themselves and others more often. You see it with BRs and heroism already. We used to horde them, they are used much more freely today since they be up soon, in time for next boss attempt if we wipe in the case of heroism, even with just 1 shammy in the raid.
In a way innervate will be more like chain mana potting in the old days. You'd use asap without wasting hoping to get one more later in the fight vs current innervate where 2 in 1 fight is a rare occurrence so you save till you are nearly oom hoping to snatch a few more replenishment tics while you're near bottom of all mana pools