Needing a Playstation+ account to access the beta is one of the things that would probably cause SE to drop FFXIV from the PS3 entirely since it would confound SE's ability to target the widest audience(unless they gave some sort of "preferred" status, while others would eventually gain access) possible. It's much akin to them dropping the 360 version because MS prefers to keep a Draconian grip on the gate keys to Xbox Live.

I also wouldn't expect SE to honor those FFXIII beta invite keys given the situation of FFXIV currently. But hey, they DID surprise us with the announcement of 2.0, so who knows?