<p>We're working on an application that displays information through a Direct3D visualisation. A late client request is the ability to view this application via some Remote Desktop solution.</p>

<p>Has anyone done anything similar? What options are available / unavailable? I'm thinking RDC, VNC, Citrix...</p>

<p>Any advice?</p>

I think you can still use all of the normal D3D tools, but you won't be able to render to a surface associated with the screen. You'll have to render to a DIB (or some such) and Blt it with GDI to a normal window HDC. RDC/VNC/Citrix should all work with this technique.
Performance will definitely suffer - but that's going to be the case over remote desktop anyway. In fact, if I were you, I would mock up a VERY simple prototype and demonstrate the performance before committing to it.
Good luck!