The situation hasn't changed. Your only two choices when using multiple monitors through an RDP session are the
/multimon will treat each screen as a separate display just like you would have on the host. You get snapping/clipping capabilities, but the downside is you can only use ALL of the screens for this.
/span allows you to use only two of your three screens, but the downside is that it's one big rectangle that spans across more than 1 screen. You lose each screen's identity as a separate, distinct display.
You can modify the local group policy on the target computer to specify a maximum of 2 displays for use with the
/multimon switch. I don't know what that would look like on a 3-screen display however. I suspect the 3rd screen would just go black. You'd have to play with this yourself.
You can get to the local group policy by hitting Start -> Run and typing
gpedit.msc. The setting you're looking for is Computer Policies\Administrative Templates\Windows Components\Remote Desktop Services\Remote Desktop Session Host\Remote Session Environment. Set
Limit Maximum Number of Monitors to enabled and specify 2.
NOTE You do this on the host computer (the one you're connecting to), not the client.