[brigade]

The "serious advances" is DSC, which the XDR is already using to support 6k over a single DisplayPort HBR2 link. Which, as others mentioned, can be carried via USB-C alt-mode in addition to Thunderbolt.

6k 120Hz and 5k 144Hz are both possible over a single HBR3 link with DSC. Such monitors don't exist because the panels don't exist; rather the closest panel for sale is perhaps the 5120x1440 at 240Hz in the Samsung G9. Which has the same bandwidth requirements as a hypothetical 5120x2880 at 120Hz.

If you want 240Hz at >4k, or 8k 120Hz, then sure that exceeds existing DisplayPort 1.4 and ThunderBolt 4 bandwidth capabilities even with DSC, and you'll need the upcoming DisplayPort 2.0 link rates. (or DSC+chroma subsampling)