Modpacks take time to test and balance. Just because some mods have moved to 1.8 doesn't mean that it is time to completely abandon 1.7. Several mods will always lead the charge in updating to a new version, and several more will linger behind, with still some never making the leap at all. This happens every time Minecraft makes a major version.
Take a look at the timeline from this last update. 1.6.4 was, at that time "the golden version for Minecraft modding" with many authors wondering if it would be worthwhile to update, as it meant they would have to rewrite large sections (or even all of) their code. A few were quick on the uptake, while many, including a few heavyweights, decided to use this chance to make some large changes (ie Thermal Dynamics). The pack makers had to see not only who had made the leap, but who was worth waiting for. The gap from 1.7 launch to Infinity was quite substantial, and it wasn't even the first pack put together on the new version.
Moral or my story? Trust these guys a little - its what they do, and it isn't their first rodeo. Don't rush them to put out product now only to say they half-assed it later. Be patient. In the meantime, try to assemble your own 1.8 pack to play with. Nothing is stopping you from being your own catalyst for the jump.
