Magical Focus

You shan't recieve either. Ars Magica is purposefully vague in some areas as to be able to incorporate a variety of styles of play.
You know my view. Do what works for your saga. In my saga, I would allow a vis focus, ut it only applies to spells and enchantments that target vis.

on the side, the wands thing is cool, as it is only a specific subsection of enchanted items. There is precedence in RAW concerning familiars (a focus in familiars or the type of animal the familiar is contributes to all enchantments to the bond).

This is somewhat different in that this is very limited: Bond enchantments can only affect you or the familiar, IIRC, whereas such a focus could affect anything.

Do you want a magus with a focus in stone to be able to cast a lot of Stone spells, but also enchant a pilum, heal, illusions and teleport spells in his stone wand with it?

That thread was very interesting, too bad I don't remember its name.