Not all metal frames may be built with the hydraulic brake hose routing exiting the frame at the bottom bracket. In principle, with an oversize BB, e.g. a T47 threaded or a PF30 press-fit, there could be sufficient room to route the hose through the bottom bracket shell around a 29-30mm spindle.
Per this post on the Weightweenies forum, some titanium frame builders prefer to enclose the hoses in an internal sleeve as they go through the frame tube. Recall that metal frames are built from individual tubes that are welded together. It may be too difficult to pull off an internal sleeve that goes all the way from the down tube's entry port all the way to the exit port on the seat stay.
However, not all metal framebuilders appear to adhere to this philosophy. I have no insight into how much of a problem the hydraulic hose will pose if it's not run through an internal sleeve.
Last, as Swifty observed, your BB shell looks relatively small. If it's an English BB shell and you have a SRAM AXS crankset, then that 30mm spindle takes up almost all the space inside the BB shell. I suspect there would be no room to route a disc hose through the space in any case.
In theory, having that small section of externally routed cable should affect the frame's aerodynamics, but the effect is likely to be infinitesimal. The section that's exposed to the wind along the downtube appears extremely short. Further, it's around the crank, and the air there is already dirty from you pedaling. Aesthetically, because that area is around the cranks, it may be hard to notice the external hose in that section. It is true that most performance carbon frames have full internal routing. Nevertheless, there are both objective and subjective reasons that this is unlikely to be a big deal.