Inserting signatures in SBTMH can be optimized: The current implementation finds the next available leaf position and puts the signature in it. This can lead to longer searches, since similar signatures might end up very far apart in the tree. By inserting signatures based on similarity, the search can potentially be pruned earlier, reducing runtime.
IPFS continues to evolve, and a promising technology is IPLD, a data description format that maps well to the way SBTMH are saved: a JSON file with a representation of the tree, where each node points to an IPFS objects.
Another interesting IPFS technology for the signature calculation service is a PubSub implementation that can replace Amazon SQS as the event notification system. On top of decentralized storage aspects of this project, this also makes possible a loosely-coupled distributed computation system.