No, you cannot use only the I channel and zero IF. This is due to signal processing theory. An I-only signal is not analytic (i.e. it has negative frequency images). When it is down converted to DC, the negative frequency image falls right on top of the positive frequency image corrupting it. This is manifested as a low signal to noise ratio (C/No ratio), which causes reduced number of satellites to be acquired. By using both I and Q outputs and treating the signal as complex rather than real, it eliminates this problem.
Using both I and Q, and correctly implemented baseband software, there is no reason customers should not be able to acquire and track 8 or more satellites.