The albums before
Romantic Warrior were on Polydor, who never committed to a quad format, sadly - they were one of those "we're studying the market" labels who were waiting for a dominant format to emerge, and none ever did before quad died.
That
Romantic Warrior never got a quad mix is kind of surprising - before 1975 CBS was kind of trying to get anything mixed in quad that they could, but by that year they kind of saw the writing on the wall for quad being a niche format, and like RCA they moved to more of a 'only hit albums in quad' kind of philosophy. So I think if RTF had signed with Columbia in 1973 you probably would've seen some or all of their albums in quad from the start.
They probably didn't expect
Romantic Warrior to do as well as it did either, given that
No Mystery only made it to #7 in the jazz charts and #39 in the Billboard Top 200 Album charts - a respectable showing, sure, but not exactly setting the world on fire. There's also the issue of where the album was recorded and mixed - with CBS's quad output (and a lot of labels in general) you'll often see more quad releases from artists who worked with engineers who were 'quad friendly' and in studios that were quad equipped, simply because it was cheaper and easier to do a quad mix at the same time as the stereo mix with the same personnel and studio. In the case of this album, it was recorded at Caribou Ranch (Chicago producer James William Guercio's studio in Colorado) which was definitely quad equipped because all the Chicago quad remixes were done there, but
Romantic Warrior was taken to Trident in London (which according to
@Stephen W Tayler wasn't quad equipped) for remixing by Dennis MacKay, who I've never found any evidence of having any quad mixing experience.
Back then, the industry was moving so quickly, with bands basically releasing an album a year, that by the time
Romantic Warrior was a hit it would've basically been too late to do a quad mix because the album would've been considered "old" and at the end of it's promotional cycle by the time they could've got one done and on the shelves. This is probably why
Musicmagic got done, on the strength of the sales of
Romantic Warrior. You see this quite often in quad, frustratingly - the hit album doesn't have a quad mix, but the less-popular followup album does: Redbone's
Beaded Dreams Through Turquoise Eyes gets done on the strength of
Wovoka having a hit in Come and Get My Love; Johnny Nash's
My Merry-Go-Round gets done on the strength of
I Can See Clearly, and Wild Cherry's
Electrified Funk gets done thanks to their self-titled debut album having Play That Funky Music on it.
Quad mixes or not, I think the Return to Forever albums are ripe for Atmos remixing - in 2008 Concord put out a 2CD collection called
The Anthology which featured almost all of their 1973-1976 material (including the full
Romantic Warrior album) and all of it was newly remixed by Mick Guzauski, who somewhat recently did the Atmos mix of Daft Punk's
Random Access Memories. So presumably somewhere in a vault are the already digitized multitracks of all those albums - all it would take is UMG (for the Polydor albums) or Sony (for
Romantic Warrior) to throw a bit of money at the project and get Guzauski to revisit this project in Atmos.