Just a thought. There are some important books out there which deserve good indices. The prime example, which has frustrated me innumerable times, is Daniel Sperber's
seven-volume book, Minhagei Yisrael. There is a huge amount of information there. Much of it appears as BTW footnotes in random places, or scattered in the addenda to the later volumes. It takes ages to find what I want, and I'm never sure there isn't some crucial passage hiding somewhere I didn't notice.
If Sperber intends to publish additional volumes, and I certainly hope he does, perhaps a good way of keeping the index up-to-date would be online. This worked well for another book
that kept coming out in clumps.
By the way, a slightly edited version of one of my postings is now on Jewschool