Here are a few things to consider to address this issue:
1 - I think active voting power will quickly reach into the 75+% level very soon after periodic Followee confirmation is implemented. Hence, this concern will likely be resolved naturally.
2 - Dfinity holds voting power in many neurons according to @diegop. If you find that you have too much voting power compared to the rest of the NNS, then you can choose to not vote with some of the neurons.
3 - To be honest, I would rather start with Dfinity having too much voting power in the very beginning than to continue with the voting participation imbalance that is currently caused by default following on All Topics. I think this is a minor issue and would be glad for Dfinity to have too much voting power if active voting power is adopted as the reference point for voter participation. I like this enhancement a lot.
4 - There is always the option of setting up some of the Dfinity neurons to follow other public known neurons in order to ensure that the Dfinity neurons are maximizing voting rewards during a transition to increased voter participation. Since Dfinity owns their voting power, they can choose to follow any other neuron for any reason they want just like everyone else. You could even use this as an incentive for new public neurons to surface by giving them a voice.
Those were just several ideas that come to mind to address the concern. However, I’m not really that concerned. I think the issue will quickly go away on it’s own.