SegWit and SPV-mining. What if...? Is the following scenario valid?


Some unhonest segwit mining pool takes top-1000 segwit utxo and mines a block at height N with a transaction which transfers all funds to his p2pkh address
This block does not have segwit data portion, but it can be broadcasted to all non-segwit nodes on the network
All other pools have a dilema - wait the segwit data associated with this block or start mining block N+1 on the top of N
What if miners will use SPV-mining on the top of this block? They will create blocks at heights N+1, N+2... etc without checking the segwit-validity of block N


Also asked here: https://bitcointalk.org/index.php?topic=1434842.0
Yes, they can do that.
Correct, though the switchover requires a 95% threshold to make the chance that old nodes see confirmations on such blocks very small.
Segwit nodes never accept blocks that have a witness commitment but no witness section. Either the block must not have a commitment (in which case it will be invalid, as script validation fails), or it is outright not accepted (because there is missing data; similar to a block with missing transactions isn't accepted).
Miners that don't validate a block before mining on top of it violate the security assumptions of the network. We can't prevent them from doing so (with or without segwit), but that is one of the reasons why block propagation and block validation needs to be low-latency: so that the potential advantage miners get from SPV mining is not too significant.