They do seem nice, and I think I may get the dev kit some time just to play with it. I was waiting for their release ever since I saw the series listed on the LPC5500 series page. But the LPC55(S)3x product page, data sheets, dev kit and other documentation were made public only 20 days ago (April 1st). I haven't seen any stock of either the micro or the dev kit since, so I would be surprised if anyone has been able to try them yet. I suspect that may take a while.
Incidentally, the thing that I find a bit confusing is how the named the dev board. In the other LPC55(S)xx series they all have names like LPCXpresso55Sxx / LPC55Sxx-EVK. The S means the chip version has the optional security features. Except with the LPX55(S)3x series they somehow ended up naming the kit both LPXpresso55S36 and LPC5536-EVK (non-S). Then there is a "Getting Started with the LPC55S36 Evaluation Board" page that does talk about a LPC55S36-EVK (instead of LPC5536-EVK). I haven't yet found a clear statement in any of the documentation about which micro is actually mounted on the dev kit, the LPC55S36 or LPC5536. Or that they may have two version of the board.