I'm not suggesting a traited global speed increase on DRK. What I'm actually doing is turning Delirium into a modified version of Enshroud on DRK. If you add a second action (in this case, Torcleaver) that directly combos off of Bloodspiller and reduce both GCDs to 1.5s, then you're essentially turning Delirium into a 6 GCD burst. Every two blood GCDs you gain a free Edge/Flood that you weave into the mix.

As much as I liked Blood Weapon's speed boost, I've actually grown to love having a few dedicated 1.5s GCDs so much more. It just feels good.

I don't mind Living Shadow conceptually, but the design concept feels a bit clunky because of the summoning lag. It probably would have been better off going the Bunshin route, which is somewhat in line with what you've suggested.

I do like the idea of interplay between MP and blood. I've been advocating for blood moves to generate MP and vice versa since Stormblood. MP is a slightly awkward system, however, and I feel that jobs are better off if they just use a unique dual resource system. It becomes a bit more complex to design around MP because you also have to account for passive ticks that continue during downtime periods, which ends up with generation either being too fast (Stormblood) or too slow (post-Shadowbringers). I think blood is a more predictable system, though, so building from blood to MP probably makes more sense than making it a recursive loop.