So, the 25% bonus to Legendary drops in Nephalem Rifts is multiplicative and will actually stack with the scaling Legendary drop rate bonus in Torment 1-6.
This means if you're playing through a Rift in Normal-Master, you'll have a 25% bonus to Legendary drops. If you're playing through a Rift in Torment 1, you'll have a 43% bonus to Legendary drops (1.15 * 1.25 = 1.43). If you're playing through a Rift in Torment 2, you'll have a 65% bonus to Legendary drops (1.32* 1.25 = 1.65). And so on.
Hope that helps clear some things up a bit. (Also, I really hope my math checks out. >.>)
Note that we're going to continue to keep an eye on Rifts and how rewarding they are (or, more importantly, how rewarding they feel). We've already seen some great feedback from players on that topic that we're taking a look at now. This buff is just a small change we could make quickly, and we're definitely looking forward to your feedback over the next few days.