Pretty much all high-end client SSDs have no issues saturating the current 6Gbps SATA interface. We've talked about a move to PCIe based SSDs but these are the connectors that will do it.

On the right you have SATA Express, which will deliver up to 1GB/s on PCIe 2.0 and up to 2GB/s over PCIe 3.0. On the left there's the eventual landing place: the SFF-8639 connector, good for PCIe x4 with speeds of up to 4GB/s (PCIe 3.0).

Most client machines will likely use the new NGFF card form factor, but for huge capacities and performance (e.g. servers in the enterprise) we'll see a move from SATA to SATA Express to the SFF-8639 connector over the next few years.