The biggest hurdle remains that those running non-mining nodes carry the burden of helping to secure the chain while receiving no economic reward.  They gain benefits like privacy and not relying upon trusting others.  But, financially, there's no recompense for the service they provide.  As such, they will only offer to carry a greater burden at a time of their choosing and not merely when others complain about it.

Make all the arguments about decentralisation, propagation and politics you want, but all those points largely fall by the wayside the moment you start asking others to do more than they're already doing, just so it might benefit you and give you lower tx fees.

When the majority of nodes are willing, that's when it'll happen.