Can more SE affiliated Music Composers contribute with music to this game?

[Enkidoh]

Composers from FFXI, Nier or how about Yasunori Mitsuda contributing with something? =)

Is is the price that they charge thats preventing them or Yoshi P really wants a close circle? Different composers can give a different feel and touch to the game.

The only FFXI composer who actually hasn't already contributed to FFXIV's OST is Kumi Tanoika, as both Nobuo Uematsu and Naoshi Mizuta have worked on numerous tracks for FFXIV already. SOken might be the Sound Director, but he's not the sole composer for the game - SE haven't had a FF title that has a soundtrack solely composed by one composer for years (spin offs don't count).

Really though, it's apples and oranges here - as you said Uematsu and Soken's compositions for FFXIV is perfect enough, and having other composers contribute just 'spoils the broth with too many cooks' so to speak, as the soundtrack loses cohesion. But that is just my own opinion as they say.

[Fenral]

Soken might be the Sound Director, but he's not the sole composer for the game

He is and he isn't. 1.0 was originally scored solely by Nobuo Uematsu, making it his first solo project in the series since FFIX. When the meteor hit, Masayoshi Soken was brought on as sound director and composer, with a number of other S-E composers contributing in places as well, but never more than one or two songs. While most songs from 1.X did end up reused in 2.X, the composition of new music specifically for A Realm Reborn was handled entirely by Soken.

Likewise, with Heavensward, the theme song is by Uematsu, but the new score itself is entirely by Soken, occasionally borrowing melodies from Dragonsong but otherwise sticking to his own compositions. So while some tracks in-game were contributed by other composers, the only active composer assigned to Final Fantasy XIV is Masayoshi Soken.