Hell yes I would buy a case without 5.25" bays, too many cases are being limited by the obligation to have 5.25" drive bays incorporated into their design.
1. Windows (or any OS) installs so much faster from any decent USB thumb drive
2. most software these days can be downloaded and installed direct from the internet with ultimately far less hassle than having to manage what will eventually become physical clutter. Major game titles are also often preloadable allowing users to play immediately upon release without having to go to the store and wait in line.
3. even if you still need a ROM drive, USB drives are more than acceptable in my experience, there are even external enclosures to convert internal 5.25" ROM drives if you find the native USB versions to be too slow (as they're typically designed more to be slim and compact than for blistering speed). Heck, I'd even argue that external ROM drives are preferable as they allow you to tuck away your case and save desk/work space.
Really, the only things I even consider for the 5.25" bays are external panels such as fan controllers (which I feel are mostly fluff anyway and haven't used them in years) or mostly for 3.5" drive expansions for more HDDs
Without the obligation of adding 5.25" bays, cases could be more compact, have much better internal expansion options for things like water cooling, larger expansion cards, more room for HDDs, better airflow, etc...