I have mixed feelings about the whole thing.
The indexes allowed for 8e to be released faster. GW was able to make "play now" rules to ring in the new edition without having to wait until all of the armies were properly updated. The indexes allowed players to get in and play a more "watered-down" version of the game and to complain to/praise/report problems to GW. They were able to take this information and apply it to a more finalized rule set. In the end, the codexes will come out over the course of a year (or more, since they seem to want to be VERY thorough), meaning 8e would have been delayed by that long.
It would have been nice, however, for GW to come out and say "The indexes are temporary and will become outdated when the codexes are out," and then listed tentative release dates for the codexes. Classic Space Marine players probably would have passed on the index (maybe), while almost everyone else would still have benefited from the indexes.
Hard to say, though. I like the index, personally, but am a bit "meh" about having to buy yet another book in the coming weeks.