The link to the previous discussion is helpful, even though I don’t agree with the logic to dismiss the DVD iso.
CDs/DVDs were an inexpensive ‘business card’ used by many to promote their wares and get the message/software into the hands of as many people as possible for them to try out. This was done by several linux distributions (Slackware is the most impressive, text based install no xorg stuff) and many non-profit orgs and even for-profit companies. Ex. SUSE, Novell, Oracle, Firefox, Thunderbird, …
even evilCorp put out very nice (but useless) eye-candy CDs/DVDs. If the idea is to get the Qubes OS into as many hands as possible so they can see how it can work for them, then committing to Blue-ray, Double-Sided and USB install mediums is a big barrier. Making DVD coasters is much less expensive than Blu-Ray and Double Sided wind chime ornaments. Using USB is complete overkill for a temp storage medium better applied to other tasks. Especially if all that is at hand are 256GB usb ssds.
I appreciate what the development team does and has done. This looks like something worth giving a try. But this whole installation work-around is a royal PITA. No disrespect intended.