The biggest risk is that an exchange would be on the old fork, accept a deposit that wasn’t accepted in the main chain, the user would exchange it for another asset and withdraw. It is likely the deposit would be recorded in the main chain as well, but with nodes using the new protocol banning old protocol nodes, it may not be propagated in both forks. Due to the seriousness of such an outcome, a very high degree of consensus is appropriate. 85% might be a reasonable figure, but 75% is clearly dangerous. We can get the consensus as people eventually upgrade. Automated upgrading based on a signed instruction from a data feed you choose to subscribe to is planned as a medium high priority. This will make protocol consensus even easier. I believe we can make data feed subscription the default behavior for new client installs in a way that doesn’t favour any particular data feed, but just mirrors their popularity in the wild.