"However, the typical audiophile mantra is to demo for yourself to find what subjectively “resonates” with you. Can’t do this with a kit."
Not true in all cases. The GR Research forum on audiocircle has a sticky up on top where people offer auditions of the speakers they've built. There's lots of people willing to help, if you're interested enough to pursue an audition.
I haven't chased it down, but I'd be surprised if CSS didn't offer some way of hearing their speakers before ordering.
"Usually it's the box that is hard to make. A strong, non resonating speaker cabinet takes a lot of bracing and wood working skills."
..well, we definitely don't want to try anything outside our little bubbles. CNC-cut flat packs are offered from the two kit vendors mentioned above. It only takes modest skills, and a minor amount of common tools, to assemble them. People (that have never done it before) do it all time. You just have to want to do it. There are a ton of build threads on the GR Research forum. CSS builds are discussed on other forums(parts express, what's the best..).
Resale..yep, there is a market(usually within audio forums as they are familiar with the models and vendor), but it'll be harder than selling a name-brand speaker. But, say you buy a name-brand speaker for..$10K. That speaker has..I don't know..$2500 worth of parts in it?? Then one day you need to move on from that $10K speaker and sell them for...$6K? Well, that $4K hit you just took more than covers the cost of a very good kit. So, the moral of the story is we all need to pay to play. You can buy a speaker kit for $2-$3K (that'll sound like a $7-$10K set of speakers) and sell it eventually, after enjoying them for years, for.. $1500? Seems like a similar story compared to the buying and selling of a name-brand speaker.
Disclosure..I'm currently building an older model (offered & popular 12+ years ago) GR Research speaker (Super V) from scratch, no flat pack. I'm a somewhat seasoned woodworker. I've seen a number of sets of these built up Super V kits sell over the years for around $2K+. The parts for this speaker kit didn't cost much more than that.
All of the info I've offered here is on the web if you do some searching.