Broad strokes, you would expect to see a withdrawal of funds from the market by anyone following equal weight funds. New entrant means you have to pull money out of existing stocks to re-allocate to the new entrant to maintain equal weights.

It would be visible at a macro level, you’d see a higher sell volume and probably a drop in price as all the equal weight funds rebalance.

There’s a heavy motivation to be the first mover here, because those sells will cause a supply spike and price drop. By being the first mover, you can rebalance before prices drop.

I don’t have sell volume data, but we didn’t see price drops so either a) the market did not believe and no one rebalanced, or b) few funds rebalanced, and the other funds disbelieved enough that they thought the risk premium was so small they could buy at a slight discount and profit, balancing supply and demand.