You wrote “The challenge is that no one has figured out how to achieve a global ordering of transactions in a DAG (well, maybe, stay tuned here). The lack of an ordering-of-transactions capability makes trading and financial applications extremely difficult.”
That’s exactly what Syscoin’s Z-DAG Protocol does. Z-DAG uses a network of bonded validators (masternodes rich in resources and sharing fat interconnectivity) as high-throughput relay with tx ordering in the mempool. After this form of pre-PoW consensus facilitates the expected near real-time transaction, the transaction enters SHA256 BTC merge mined PoW for high finality… Now check this out: the tokens are re-transferable prior to that PoW finality — DAG consensus is maintained and proceeding TXs are likewise rolled to PoW. All in a manner at a “sweet spot” on the decentralization spectrum without need of any central ‘watcher’ servers which plague typical DAGs (thank heavens for masternodes). It all already works with Syscoin Assets/Tokens. Both Z-DAG and Assets are functioning and have been since release of Syscoin 3, May ’18. The protocol was invented by Jag Sidhu, Lead Core Dev of Syscoin who is well-respected by devs in the space. Now Syscoin 4 is coming during this quarter and will tie all of that into Ethereum Virtual Machine. Whiteblock is in process of testing performance of the protocol, and thus far their responses to preliminary results sound very promising.