Thanks a bunch for your answer!
a. I think you will have some problems with the sleeve moving separately from the rode. Normally the sleeve and line have similar elasticity.
I was thinking of checking the give in the core line, and then make the sheeve a given length (depending on how long the protective sheeve will need to be - could be 60 feet, for example), and then attach the end of which, 25 percent lower down on the core - in essense "pushing" it down a bit so it doesn't influence the core rope.
b. I think you will need some chain--at least 10 feet--to hold the shank down during setting. I have tried going without chain for small boats and it is a problem. Even more so with high-mod lines, which generally less dense than nylon (float).
I was thinking leaded line from Liros to hold down the shank, but now when I think about it, I could test the cut and abrassion resistance by attaching a bigger sleeve around a piece of chain just to test it.
Consider using some chain backed by high-mod and using a VERY long snubber (50 feet). Multihull sailors understand your point. With that sort of a performance boat, non-conventional solutions must be investigated. My last boat was an all-Kevlar cat and carrying much chain was out of the question.
The boat will have a (carbon) bowsprit, but in an oldstyle, with bobstay, whisker stays and so on, so I will have to use a bridle or a snubber even with chain. I don't think I want the actual anchor rope to be high mod, although it would save some weight. There's a hole in the stem where the bobstay is fastened (it's actually fastened with dyneema), which ought to be big enough to be able to attach the snubber to. And it's a real low boat (it has no cabin or anything), so I will be able to reach that from lying on the foredeck.
Now that you have put it into my mind, perhaps I should go look at some multihull forums to see what they do. Do you happen to know some (I'm really not well versed in multihulls, having never been on one, except a hobie cat decades ago)?