Roadmap - BcacheWiki

Better IO tracking, allowing sequential IO to bypass the cache
Write behind caching
Journalling won't be necessary to guarantee data integrity for write behind caching, but will provide better performance on synchronous writes
Multiple cache devices
Mirroring dirty data when using multiple cache devices
Checksumming
There's room for a lot of experimentation and potential improvement in the various heuristics. Right now the cache functions as an LRU, but it's flexible enough to allow for a lot more. Potentially, we can retain data based on how much real time it saves the backing device, calculated from both the seek time and bandwidth.
Perhaps tiered storage