I just wish Yahoo would open source Everest (their multi-PB column store DB based on PostgreSQL) -- this would be ideal for building an open source Splunk competitor.
Re. an open source log indexer: Agree, this is a space that will eventually become dominated by open source tools, used particularly by startups and small businesses. I think most people ignore this use of a MapReduce-like framework because they conceptually understand how it could be used, but 99% of all work is in the implementation, not the idea. And as of yet, I don't believe there has been a specific implementation beyond what companies like Shopify are doing where they add nice GUI tools on top of awk and grep (which admittedly is probably good enough for most people / business on this forum).
If you have huge datasets, we'd love to hear from you. If even to chat for a few minutes about what your data looks like. Ping me at info@drawntoscale.com -- maybe we can help!