If the majority of nodes aren't relaying them to other nodes (current state), how will the miner receive the transaction? Unless it's relayed directly to the miner node ala LibreRelay.

Let's say 5% are running Core v30 and 95% are running Core v29. What are the odds a spam tx gets relayed to the miner node that hits the next block?

If one was running v30 with the new default datacarriersize, but the majority were on older versions, wouldn't it be the v30 node who's fee estimates would be off?