I think many people want that, such a shame it will not happen.
Square Enix said themselve that the SMN/SCH Exp share was a mistake and that they don't want to do it ever again.
BUT, what if they manage somehow to "split" without split ? Why not separating completely the SCH from the Arcanist, but keep all the low level spells exactly the same ? Making a difference between Codex and Index (SMN book will be equipable by Arcanist and SCH Book will not be able to do that) and removing the "Exp share". Maybe then, we could have "Similar" classes like what you proposed.
Now into what you propose :
Bard having a Ranger counter-part seems a good idea. Maybe turn the Bard into something more support like (why not even a completely new healer,) while the ranger specialise into DPS. The perfect exemple for the "Bard" healing, would be to look at FF4's character : Rosa, A white mage who use a Bow. That can be a design to use.
For Warrior, having a Berserker counter-part will only be logical. Pretty straight forward I must say, but effective.
Dragoon is a quite odd class to mix up with something else. A Sentinel, in my opinion, would be something like a "Hoplite" style, meaning a long lance and a shield, and that doesn't allow to be a "similar class". This one surely isn't easy to mix...
Monk and Skirmisher... I think you'll need to explain a little more what you think on this one, cause I really don't get it. To me, they have nothing in common.
White Mage for healing, and Geomancer for DPS is actually doable. Considering the White mage skill move, it use pretty much Light and Water in order to heal and protect. Geomancer could use more Earth in order to deal damage, It can even have some supportive heal or protection, because Earth Magic can be pretty vast to explore.
Paladin with a Duelist counter part, again just like the warrior and Berserker pretty straigh forward. The only difference, would be to drop the shield to focus on a gameplay that has more nerve, and speed approching the Samourai