Massively reports that Turbine is releasing an official Mac OS X
client.
http://massively.joystiq.com/2012/08/22/lotro-lifts-rohan-nda-unveils-mac-client/
Rumors also hint that a DDO (Dungeon and Dragon's Online) client may
be in the works as well. Nothing on official client for Linux that I
can find.
That is correct. I have been beta testing it since the Riders of Rohan Beta began.
It is a full Mac Port, not Cider, Wineskin or similar travesty, and it works quite well. It is full OpenGL support, not DX. Only supported under Lion (10.7) and Mountain Lion (10.8). And, needless to say, it will only run on those Macs which are capable of running those versions. NO Snow Leopard support!
At this time (we just started Beta 5.3 last night - 9/27) both clients, the Mac Client and the Windows Client still have serious crash to desktop issues. This is the main reason why the release of RoR was delayed until 15 October.
Riders of Rohan marks is a series of significant technology changes, not just upgrades to the Game Engine itself, hence the crash issues.
(It does run under ML 10.8.2.)
As of Beta 5, (I have not verified it yet with 5.3, which is patching as I type), the Riders of Rohan Client is not known to run under ANY version of Wine -- on Mac or Linux.
As for a DDO client, I would assume that will follow the LOTRO Client, once the bugs are worked out. DDO, in fact, had some of the underlying changes implemented back in the spring, apparently as "testing" for inclusion in LOTRO. While similar game engines, LORO is a much more demanding environment than DDO.