Instead of only the BTree vs. BTree durable comparison in qps, I think it would be helpful to add plots with the following information:
1) Increase in write speed gained from batching. Specifically, in section 3 you mentioned that the constant time overhead was your motivation to design the batching system. In a world of SSD writes, the usefulness of batching comes in to question. To see a gain realized would put this question to rest.
2) The effect of batching on the write-time of clients. The write up focuses on reducing the db's workload, which is the correct problem to focus on as that is the bottleneck. But there is a cost on the client which comes waiting on the writes of other concurrent clients. I would assume that your solution actually reduces the overall cost for clients as it reduces the burden of serialization, but it would be interesting to see this data.