Great article in terms of raising the point on Apollo 6, since even in general spaceflight discussion it is usually forgotten in terms of the kind of issues that were exposed because of the pogo oscillations on both the S-IC and the S-II (not to mention the other issues).
Just to lay out a quick history for pogo on the Apollo Program in terms of the modifications post-6, in the case of the S-IC, the issue was actually identified as having also occurred on Apollo 4 in terms of the pogo effects there, and b/c of the delays in having to modify already manufactured stages, did a modification to the engines to enable the 'detuning' of the engines so it wouldn't occur. The S-II... was another matter and had pogo issues from the center engine... which was mounted on the engine crossbeam. A suppressor was developed by the time of Apollo 13 but was deemed fine not to install it because of difficulties involved in it since it was already stacked... but would sprout up to be an issue with an up to
thirty-four g's of force detected before the engine shut down b/c of low pressure. [1]
I think overall if in the event of Apollo 6 having had worse issues as a result of the pogo issues, there would have been a reflight of Apollo 6 with an entirely uncrewed vehicle, and Apollo 8 as we know it not happening, considering it only emerged because of the delays from the Lunar Module, and both the CSM+Saturn V being ready (you might see depending on how the test flight goes and if need for
another uncrewed test flight, the originally proposed dual launch Saturn IB rendezvous w/ the CSM and LM). There was historically speaking, a serious debate on the matters of whether or not there
would be a need for a reflight of Apollo 6 considering the variety of issues encountered (pogo issues, loss of one of the SLA adapters [2], S-IVB failing to restart) but was decided in the end to just fly Apollo 8. I don't really think there'd be much more impact besides potentially Apollo's landing shifting to the right and maybe happening a bit later in the year depending on what happens.
I don't think imho that you would've seen a LoC event happen regardless as a result if the pogo issues weren't fixed in the case of the S-IC (seeing as you still had the LAS), with the question of an S-II abort (which would've been via CSM at the point in time) imho being survivable but potentially rather rough?
[1] The information on pogo effects for the Saturn V are sourced from this document,
here.
[2] There's a discussion on the actual abnormal structural behavior during Apollo 6,
here.