I see. To clarify, TokuMX's indexing technology doesn't try to improve specific queries or patterns - it simply makes general index maintenance significantly cheaper and less space intensive, so your application can define the indexes it needs, not just the ones it can afford.
Interesting perspective, but it turns out that the opposite is true. Using better indexing is a general improvement to database performance and manageability.
There have been very informal talks with the folks at 10gen. The topic of getting merged or not will ultimately come down to what users want. Commercialization will start with support, much like what 10gen does for regular MongoDB and what we do for TokuDB.
As for licensing, TokuMX embraces the spirit of open-source and we're confident our open-source licence plays well with the AGPL.
TokuMX is indeed a complete product, not an experiment. We're proud of it and ready to support it yesterday :)
I completely agree that pluggable storage engines are an interesting topic. But we went the integrated route (ie: no storage API) probably for the same reason: things get simpler and easier to implement when the stack is shorter.
Most users should expect a big reduction in disk space. Depending on your data and level of fragmentation with regular MongoDB, you could see ~4x-20x reduced disk usage.
"Fractal Tree" is indeed a marketing trademark. But the algorithms used are not necessarily secret. The implementation is similar to the cache oblivious streaming btree: http://supertech.csail.mit.edu/papers/sbtree.pdf
Of course what's not described in the paper include: transactions, mvcc, logging/recovery, parallelism, etc. Those are really interesting topics as well.