It might be useful to allow Hot Rod clients to start transactions within Hot Rod servers. The possibility of clients participating in the actual transaction, i.e. being an XAResource, should not be imposed since this might be less than trivial to achieve in non-Java environments. The alternative would be to allow clients to start Hot Rod server local transactions only.
This would require enhancing Hot Rod spec to have some begin/commit/rollback commands that return a tx id, and for clients to be able to send this id as part of each command that should participate in the transaction.
Pitfalls to avoid include avoiding a transaction to be propagated over several Hot Rod servers. IOW, to simplify things, if a tx is started in server A, all ops within that tx should be directed to tx. Load balancing could still happen but would need to be tx sticky.