If we wanted to encourage spellsword builds, then we could always try implementing armour with reduced ASF. Say, a Mithril Chain having 10% ASF instead of 25-30%. I play a Bard that casts in leathers. I just accept the spell failure as a necessary and minor risk for my continued good health. And now, if we were to craft these things with the smithing skill, that opens up more spellsword builds (at a ludicrous price to the purchaser no doubt), we've effectively tacked what I believe to be a balanced spellsword solution onto an existing craft, and it only requires 8 new items (the armours, mithril ore, mithril ingot), and (likely small) amendments to one of the existing crafts.
Of course, I could just be talking nonsense, but I've always wanted to recreate my P&P Ravenloft charater, a Swashbuckler/Duskblade hybrid, in spirit so I've put a bit of thought into this one.