It's really striking to me how big the range of opinion is here. Here are my thoughts on some of the classes:
Assassin: Make it a class if you like, but (in my opinion) there is really nothing that distinguishes it from a rogue or a fighter/rogue. Poison use is one; sure. disguise of a limited palette of shadow spells. Neither of those are enough, and (in my opinion) spells only point to the weakness of the basic concept. Which leaves Death Attack. Now don't get me wrong: death attack is kewl and all, but NOBODY wants to give a save-or-die power to the DM. Which leaves us with a choice if this is given to the assassin:
(a) the GM can have the party hunted by an opponent with assassin levels and risk having their characters instakilled.
(b) PCs receive plot immunity from instakill (lame double standard)
or (c) PC assassins don't have an instakill power.
For me, (c) is the clear choice. And whether it's a hobbled independent class or a developed rogue scheme (giving poison and perhaps some non-magical disguse abilities), both are better than the implications of introducing save-or-die to the game.
I liked the suggestion above of making the Ranger built around CON.
Warlord. Bringing back the Marshal's auras is a good call, I think. I think it would be great to have the Warlord based around Charisma, but Paladin offers another Charisma-Strength combination. And, as Li Shenron wriites, the auras also naturally fit under the Paladin. But accepting premise (1) of the OP, there is conceptual overlap.
Finally -- if Druid is to have shapechanging, it needs to be severely constrained to a certain class of animals -- none of the ridiculous possibilities permitted in 3.X -- too much work for the GM, and it actively took fun away from other players, as the the nature priest turns into something no one has seen in nature. My preference has always been for the non-shapechanging Unearthed Arcana variant -- it gives a bit of monkishness, a bit of range ring without blocking either of those, and stops the druid taking over combats. Really fun to play AND to have someone at the table with you play.
Assassin: Make it a class if you like, but (in my opinion) there is really nothing that distinguishes it from a rogue or a fighter/rogue. Poison use is one; sure. disguise of a limited palette of shadow spells. Neither of those are enough, and (in my opinion) spells only point to the weakness of the basic concept. Which leaves Death Attack. Now don't get me wrong: death attack is kewl and all, but NOBODY wants to give a save-or-die power to the DM. Which leaves us with a choice if this is given to the assassin:
(a) the GM can have the party hunted by an opponent with assassin levels and risk having their characters instakilled.
(b) PCs receive plot immunity from instakill (lame double standard)
or (c) PC assassins don't have an instakill power.
For me, (c) is the clear choice. And whether it's a hobbled independent class or a developed rogue scheme (giving poison and perhaps some non-magical disguse abilities), both are better than the implications of introducing save-or-die to the game.
I liked the suggestion above of making the Ranger built around CON.
Warlord. Bringing back the Marshal's auras is a good call, I think. I think it would be great to have the Warlord based around Charisma, but Paladin offers another Charisma-Strength combination. And, as Li Shenron wriites, the auras also naturally fit under the Paladin. But accepting premise (1) of the OP, there is conceptual overlap.
Finally -- if Druid is to have shapechanging, it needs to be severely constrained to a certain class of animals -- none of the ridiculous possibilities permitted in 3.X -- too much work for the GM, and it actively took fun away from other players, as the the nature priest turns into something no one has seen in nature. My preference has always been for the non-shapechanging Unearthed Arcana variant -- it gives a bit of monkishness, a bit of range ring without blocking either of those, and stops the druid taking over combats. Really fun to play AND to have someone at the table with you play.