The problem with a punishment mesmer, defensive juggernaut anything, and turret engie is that they result in degenerate gameplay. Turrets can't be allowed to succeed in PVE (see: Lake Doric), and none of these class fantasies can be allowed at all in PVP.

Turrets and juggernauts turn into turtling bunkers that either grind play to a halt or turn into raid bosses, and the only way to balance them is to essentially make the style of play unfun for the person who wants it. "Being unkillable" or "controlling this space" can't be supported in a competitive game mode. Now, you can balance this by just splitting everything and making the specs unplayable or wildly different in competitive modes, but that means you're now devoting the dev resources to build the thing twice (for both modes), yet players can only really enjoy it in PVE. From a design perspective, that's a really poor return on investment for an elite spec.

Punishment mesmer worked in GW1 because you had much better defined roles in all game modes with less overlap, and there was ability parity between players and NPCs, so you could interact with an enemy mob essentially the same way you'd interact with an enemy player. In GW2, you can't punish a playstyle because playstyles aren't that well defined, and you can't create a niche for hex gameplay because they gave everybody else the mesmer toys (see: Torment and Confusion). If you try to make a spec that depends on them even more than certain mesmer specs already do, the byproduct will be turning revs into gods (again). There's also no energy denial in GW2, and you can't give a player a bar full of interrupts because everybody already has as many interrupts as the game can support without being catastrophically unfun. GW2 is just the wrong kind of game for GW1's mesmer--like a lot of things that were better in GW1.

If you ask me, we don't need more elite specs. We need more non-elite specs--stuff we can combine more freely with what we already have--and we need the elites to be "de-elited" so that the power level of the vanilla specs have better parity with their elite counterparts. I know they've taken a pass at this before (or two or three), but it has clearly not panned out. The presence of multiple options for ranged elementalists, for example, is definitely something that needs to be supported.