Not upgraded nodes will settle for the block (since nSequence doesn’t have which means) and all different (upgraded) nodes is not going to?

Sure, that’s what occurs.

How is that solved?

The reply is similar for each comfortable fork: the consensus change is just secure to outdated nodes so long as a majority of the hashrate enforces it. If not, it’s attainable {that a} chain cut up between outdated and new nodes seems.

Think about that there’s a proportion of the hashrate that produces blocks that violate BIP68. So long as a majority of the hashrate refuses to construct on high of such blocks, the chain with out BIP68-invalid blocks shall be prolonged sooner, and every time that chain overtakes a BIP68-invalid chain, even pre-BIP68 nodes will change over to it (as a result of to them, each are legitimate).

Thus, so long as the vast majority of the hashrate enforces BIP68 (and thus refuses to construct on high of BIP68-invalid blocks or chains), outdated and new nodes will ultimately agree on what the energetic chain is.