This is correct, @Daniel Thomas , however it is important to note that the 3k per year write-off is the max write-off against OTHER income. If you have capital gains, you can use as much of a capital loss as you have gains, THEN you apply the additional 3k against other income.
Your examples are correct. I just wanted to clarify the point about the 3k capital loss. it is mentioned in your post, but I just wanted to help make that point clear.
If you have no other income to report (for example, if you don't hold a regular job), then MTM doesn't have much of an advantage. You may have a trading loss, but without any other ordinary income, you can't deduct the loss from anything.
I suppose one advantage of MTM is being able to avoid the wash sale rule, but that's not really a big deal if you know what you traded in December, break the chain, and don't trade those same tickers in January.