The main goal of Doppio was never speed -- it was compatibility [0]. It's actually a JVM interpreter at present, leading to noticeable slowdown over a native JVM. Thus, there are many opportunities for performance improvements!

A recent contributor is starting to add a JIT to Doppio, which is a step in the right direction [1].

[0] Our academic paper from PLDI 2014 has more details, although the project has evolved since then (it's now JDK8 compatible, for example): https://plasma-umass.github.io/doppio-demo/paper.pdf

[1] https://github.com/plasma-umass/doppio/pull/443