The low rider boses silver brazed are a high success type deal. Tig welding, almost 100% that you will blow them through the fork.

TIG is reasonably difficult to learn if you are in someone else's shop, and their machine is set up for bikes, and they give you some tips. If you are going at it yourself, you are in a deal where you have many variables any one of which may queer the deal (flow too high, flow too low, etc...) and you can't easily tell which is wrong until you work through a lot of stuff.

As far as weakening the fork, this is the deal. You need to place the hole in the center of the blade, which is the neutral axis at least as far a major loads. You are in fact placing the hole in a place where the load from cornering peaks, but not to worry, the geometry on that axis is like a tube section the full width of the fork. While in the other axis it is 2xs the tube section of the individual fork blade. Strength and stiffness increase to the 2nd and 3rd power of the section so the structure is plenty strong on the transverse axis, one would like to think.

The second part is that once you braze or weld in the insert it is a flange to the tube that will form a safe alternative load path. So in that sense it is one case of minor BO adding where it would mater a little that you got the job right, with silver that is relatively easy first time out of the box with an proper torch.

As far as forks are concerned, Any reasonably sturdy fork is a candidate. There isn't any FEA going on with this stuff. Forks come in all shapes and sizes, if they are in the right range they can have these BOs installed, which pretty much means any not terribly expensive or light bike is a candidate.

While it doesn't solve your practice problem there are racks that use the brake boses as an additional fixture point.