Something I didn't see mentioned (and might have overlooked... I didn't read all five pages of responses yet)....

Your brother-in-law might also consider that he will need top-quality lenses for that 61MP camera. Those will be pricey, too.

Higher resolution cameras demand lenses with high resolving power. I don't know about Sony, but when Canon introduced their 50MP 5DS-series cameras, they also published a list of "recommended lenses". For the large part, those lenses were "the best of the best".... and also the most expensive.

And if you BIL doesn't make prints larger than, say, 16x20" he'll almost certainly never see any advantage to the camera and lenses. In fact, many people who bought full frame cameras are probably using way more than they actually need. Even then, look at "pro-oriented" cameras like Canon 1DX II and Nikon D5... they're 20MP and 21MP full frame.

Bigger is not necessarily better. Beyond a certain point, it's just a waste of money.

That said, lenses are more important than the camera they're used. I'd much rather have your APS-C 80D (24MP) with a couple really good lenses... than a 50MP or 61MP monster with mediocre lenses!

The idea to suggest he rent and try before he buys is a good one.

If he decides he's just gotta have the 61MP camera and is willing to also get the lenses it will demand... Here's an Apple Mac Pro and that can handle the files very well, I'm sure!

https://www.bhphotovideo.com/c/product/1530505-REG/apple_z0w3_macpro_1480_w_bh_macpro_28c_1_5tb_ssd_4tb_ssd_2xrpv.html

And he'd be able to enjoy the quality of the images on this:

https://www.bhphotovideo.com/c/product/1527826-REG/apple_32_pro_display_xdr.html

He'll still need to get some software. And a printer?

Of course, he'll be the ONLY person who ever sees the full quality of the images, while viewing them ridiculously large on that monitor. He'll need to downsize them for printing or sharing online, after which they probably won't look much different to everyone else than your 80D's images.

I have heard rumors that Nikon was going to produce XQD cards and I have heard that CFexpress is going to replace the XQD cards and be physically compatable with one another. In Nikon cameras, will that require firmware update? During black Friday and cyber Monday I was looking for a deal on 120MB card, nothing. So, before buying a Sony XQD card, I thought I would ask what is happening now and in the months to come. I don't need another card but nice to have insurance and flexability. I do like how fast they upload large files.

My wife asked me what I wanted for Christmas. I told her my list is too expensive and I can pick up things I want for photography piece by piece as I have been doing. But she insisted that I share it with her... My list,, A light meter, not the best, but not the worst. A teleconverter 1.4 for my 150-600 lens. Transmitter and receiver for flash units. And another flash unit. I told her I don't buy new, but I shop at KEH, Adorama, B&H, MPB and get quality items for less than new. Not sure what she will get or she can get me socks. She wanted a list and that's what I would like.