I think I will start out by trying this
if the blue nut has flat edges, and the far side rack strut eyelet is slotted it could be tool free to remove.
And then maybe do the rack support like Hunter dropouts? That way you can make it adaptable to both 12 and 15mm axles.
Not sure if my 12mm TA fork is in the minority but the thread is capped and the axle can’t extend beyond the fork blade.
Had to use some washers on the head side to get an axle that was 1-2mm longer than stock to work.
Don't know what hubs you're gonna use, but you could machine some thru axle end caps together with some rack mounts.
Something like shortening these:
@Hulsroy started
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I think I will start out by trying this