Some of the "rabbit hole" items included:

1. Hibernate's main CoreMessageLogger having a dependency on JTA classes. And then MessageLoggers from other modules depending on it. Some were simple enough to just remove the extends CoreMessageLogger to instead extend BasicLogger. Some (C3P0MessageLogger) actually (re)use methods from CoreMessageLogger. I had tentatively worked around that by splitting the common methods out into a new MessageLogger interface ConnectionProviderMessageLogger (no JTA deps) that both CoreMessageLogger and C3P0MessageLogger extended.
2. OSGi tests failed. This is were decided to roll back. I am not sure if the problem is that the OSGi support needs JTA to be defined in our feature file or if the problem is just isolated to testing.