"Whatever Gene Roddenberry's original intent might have been, it looks like that by 1979, he intended the top-of-the-line starships to be Constitution-class."
The quote is correct but I seriously doubt that it had actually been Gene Roddenberry who wrote the TMP novelization (possibly Alan Dean Foster acting as the ghost writer just like he did for the novelization of Star Wars).
I also doubt this is an expression for Gene Roddenberry's "intention".
I think at this point he simply didn't mind
any more as conjectural fan speculation - published in form of Bjo Trimble's Star Trek Concordance
and the Franz Joseph publications (despite their different numbering for the sister ships of the Enterprise,
the "Constitution Class" is apparently one issue they both agreed upon) - had made "Constitution Class" abundantly popular.