PoW blocks target spacing must be higher or at least equal to PoS blocks target spacing, because this system is originally designed for "slow" PoW blocks and "fast" PoS blocks.
This sounds like one basic modification to do, changing PoW and PoS targets so there's rarely more than one PoW block PoS can orphan, and shouldn't interfere much with further future improvements.
Chain has worked without that much drama until now, if an interim targets fix can make do for a while, it may buy time while more complex improvements are evaluated. No need to risk introducing bigger loopholes trying to fix a smaller bug.