I got to thinking more about the compression factor of a full length halyard and whether it doubles the load on the mast. The compression load would not change based on the sail load, but when you tension the halyard, you would be increasing the load on the mast by that amount. The rope tension is much more than the compression load of the sale, but added together, they can be considerable. The tension on the luff track would also be equal, but you could get some major distortion of the mast if overtensioned. Of course by that time you would have the sail so distorted, that I would hope you as a sailor would be aware that something is wrong with the rig setup. Has anyone ever seen a mast failure in the race enviroment just with sail load and downhaul tension?
I suppose that if you tension tight enough you could reverse warp the mast to the fore, even if all you did was straighten the mast out. That would be extreme, but it would illustrate that you could increase the total load on the mast, which could not be good, especially with the mast warped in reverse. Now I don't know if you could tension a rope halyard to that extreme, unless using a downhaul block on the halyard, and at that point you would probably be ripping the cleats out of the bottom of the mast. Again that may be a hint that something is wrong.
Actually the real problm that you would probably encounter is not being able to tension enough, and consistently. With a rope halyard, the sailtop to sheave and down to bottom cleat distance could be variable and stretchy, not very efficient. Whereas, with the short wire halyard, there would be a fixed and non stretchy relatively speaking, distance that the sail top would be from the sheave. Then when you downhaul at the boom, the downhaul guage would give you a meaningful measure each time you set the boom.
What you are wanting to do is induce a consistent amount of aft warp into the mast, that is probably included in the sail design. If you don't accomplish that warp, you will not achieve design performance of the sails. On a high performance catamaran, this is more noticeable than on a lower performance monohull, especially in a racing environment. It may be race legal, but it would also be a handicap.
Now I am not a racer, so for my Sunday sail it may not make a lot of difference. Thanks, TnT