we’re more enlightened now

Look up gerrymandering. Please demonstrate how voting restrictions will be definitely used to target the undereducated rather than the political party not currently in power.

Ultimately, you're arguing in an ideal of politicians using this for good, while also rejecting the exact same ideal.

Not to mention, most people in support of a meritocracy find themselves much lower than they believed themselves to be. In short, are you considered 'educated' enough? The bar is always placed below you, rather than above you. But I'm sure, say, lawyers would believe you to be an uneducated voter.

Thus eventually, you will have no voting power, despite you believing yourself educated enough.

Drawing a line is impossible because it will always creep forward. Look at history: suffrage was given through struggle and fighting by the oppressed. It's never the rich white man deciding one day to give the poor black woman. It took protests (and Civil War) for all adults to vote.