Seeing how we going to have dungeon finder and that what people going to end up doing vs going to the dungeon themself and finding a party on there own world. I don't see a summoning stone being useful at all now seeing how free company would get perks and you add the perks but unlocking them / adding them to your free company house by the sound of some of the interview yoshi-p said. I think we may have a perk that would summon all free company members to person who allow to use the perk that would help everyone get there without waiting 10m for people to get ready.

I sure they be other perk if everyone dead beside one person they can use a perk to get everyone up but there a long cool down like maybe 10+hours like wow.

For friends they could easy just have what wow have that you gain more exp while with your friend and you can teleport them to your area. But having a summon stone that you can use whenever would just ruin the point of even having teleport crystal in every area and seeing how there is one in every area i don't see point in the summon stone you teleport to the crystal get on chocobo and you get to the party within 1-4m anyways so there you go.