The SO.6000 was developed purely as an experimental aircraft, with the ability to use
quite a number of different jet engines. That probably was the main reason for the relatively
bulky fuselage, that easily allowed for side-by-side seating of the 2-men crew. I don't
think, that a straight forward development into a single seat fighter would have been
as easy,as with, say the Arsenal VG 70. The fuselage would have to be completely new,
I think, with just the wing and maybe empenage to be used, so the idea may not have been
long lived.
On the other hand the original aircraft may have led itself to an easy adoption as a light
and fast communications aircraft, with the fuselage elongated to make room for 4 seats !
Pure speculation, of course ....