You mean routing DP streams to the "system" TB3 ports (i.e. the ones on the Apple I/O card and top of the case)? I don't believe so - I think that's part of what the additional PCIe lanes of the MPX modules are used for.
And it's interesting (but logical) to note: the 580X routes four streams of DP to the "system" ports - presumably because it provides no TB3 ports directly on the card itself.
All the other MPX cards provide 4x TB3 ports themselves, and they only route 2 streams of DP to the "system" ports.