There are several good reasons to move from Thrift 0.9.0 to 0.9.3, including harmonization with other projects that we link against in one form or another.
I have started to investigate upgrading, and it's not trivial. Here are the things I've run into:
1. 0.9.3 defines operator<< for all Thrift structures, conflicting with some of our bespoke implementations.
2. TAcceptQueueServer is written against an old server interface, and needs to be updated.
3. To build on all the platforms that I care about, a modern Bison install is necessary (this is an issue for native-toolchain, not Apache Impala).