Not only that. It also means, that mining testnet3 is now less profitable, and switching into testnet4 is a better idea. But a short while before that, it was the opposite, when it was not certain, if testnet4 will be reorged or not. Now we know, that those, who consider 00000000000000263393ce5f648afd53676f13d360cc9f264b89351623bf1242 as a valid block, are simply mining coins, which will vanish, after upgraded ASICs will mine an alternative chain, on top of 0000000000000016be66ab39af9f97e1294080c94d0a34cc304e391794a481bd.

In general, we are about to see at least 360 blocks reorg, at the time of writing. I guess it could be 500 blocks reorg, or even 1000 blocks reorg, depending on how many people will mine blocks, when using some older version.