It depends. If it was a 12 word seed, no problem. 24 word? That could pose a challenge.
Even it is only 10-12 words, I think it is still a problem.
It is not a challenge but it's a serious risk to access our investment.
Personally, I will never try to keep it by memorizing only. It is better to keep it on a more secure way (write them on a paper, metal, or other else).
The problem is I would find it to be risky for large amounts of money. I'd be gambling, betting on my ability to remember everything right after some time. That's where the weakness lies. I tend to forget unused things, so every day I'd have to say it in my mind before going to bed to remember it, so it's fresh in the memory. Feels like some unnecessary burden.
Yep. It is an unnecessary burden. Sure, there is no problem to memorize it but don't only keep it in a single method.
Sometimes, we already gamble investing in random coins. Why we must gamble again for the way to access it?
It is not a funny way to manage our investment. If we can't remember it, everything will be gone forever.