FCIP actually complicates things further as there's the packet load/unload, compression, spoofing etc, but if you think about it it's not really a very good fit for Peer Persistence anyway since PP requires uniform access. Doing this with FCIP would potentially force host traffic not just the replication delta's over IP since FCIP would be extending the fabric between sites.
As far as IP for sync replication it's quite possible over shorter distances (at least in Europe) and bandwidth is rarely the issue, but you have to have good quality, low latency links, no scrimping on the infrastructure between sites. But as outlined above you would only really consider this for Peer Persistence in the smallest of environments, where array ports are the issue. Because with uniform mode you have to extend the fabric over FC between sites in anyway, so all it really saves is dedicating additional FC ports for replication.