I think for Braidpool, making decisions about acceptable transactions is just as complicated as doing it for Bitcoin, because it will be a decentralized network and blockchain (DAG) similar in most respects to Bitcoin. Changing policy requires upgrading all nodes and possibly a hard fork in the DAG. We’ll try to make reasonable choices here but it seems unlikely that we will be able to support extremely odd transactions.
I’ll give some more thought to allowing miners to include a small number of non-committed bitcoin txs in their share-chain blocks. It increases share validation and propagation time but if it’s only one or two txs maybe that’s acceptable.