Best bet just their "tier-2" DDG and FFG, those interim designs, instead of the "tier-1" combat vessels now in serial production, since SAR and anti-piracy won't require the latest mission packages anyway.
All things considered, the PLAN could send a couple of the surviving Luda Class for this in protest to such cold shoulder treatment. Think about it, such low-grade access won't teach the PLAN anything new anyway.
Sending old ships would be sending a poor signal. We've heard how seriously the PLAN are taking RIMPAC. While they're not out to make themselves look hostile, they're not going to make themselves send harmless by sending antiquated ships either.
Considering ships like 054A have done exercises with USN and many other navies before and is a common sight off Aden, I expect the FFG to be an 054A. The DDG is more up for grabs, but I wouldn't be surprised at an 052C being sent, just to show that the PLAN is indeed modern.
PLAN does care about how it is perceived, despite the PLAs overall conservativeness in showing off new military developments. And 052Cs have been in service many years now, so it is hardly new technology.
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And I don't think the PLAN considers this a cold shoulder at all. On the contrary, simply being invited to participate at RIMPAC is a big step itself. Even if they were invited to participate in a more complex part of RIMPAC I doubt the PLAN would accept due to fear of revealing sensitive information during a more advanced exercise.