I'm betting we'll see completely new designs. There wasn't much (any?) overlap of vehicle designs between the OT and PT. Sure, they foreshadowed the OT vehicles in the designs of the PT, but we never blatantly saw an X-Wing or TIE fighter flying around. Even the big triangle-shaped attack ships that showed up in AotC weren't called "Star Destroyers" until RotS.

Within both trilogies, we see certain ships make recurring appearances. The N-1 fighters from TPM show up again in AotC. The LAAT gunships from AotC show up again in RotS. The Trade Federation cruisers show up in all three PT films. The OT is full of X-Wings, TIE fighters and Star Destroyers. We'll probably see designs in Ep7 that get used in the rest of the ST.