Since "aft phasers" and "aft weapons" were referred to in TOS chatter (and on-screen characters in "Balance of Terror"), it is logical to assume that both the TOS-era Enterprise and the TMP-era Enterprise both had aft torpedo launchers. Something else to consider: since TOS-era ships and the Enterprise-E both had saucer-based launch tubes, why wouldn't we assume the TMP-era ships had saucer-based tubes as well.
"Aft phaser/s" were mentioned in the TOS chatter in "Arena" and "A Private Little War", if I'm not mistaken. However, I'm not aware that "aft weapons" were mentioned in TOS chatter or on-screen.
To me the whole concept of an aft torpedo launcher looked pretty new and seemed limited to the Klingon Battlecruisers in TMP. While it's definitely an interesting (but still conjectural) thought that the circular thing between the impulse exhausts on the TOS Enterprise
could be a torpedo launcher I see no corresponding structure at the saucer's stern of the TMP Enterprise
Again, the red TWOK torpedo bay scene with the adjacent Docking Port 2 suggests an aft launcher in the stern of the dorsal, IMO. The dark "photon exhaust" area could conceal the launch tube of an "aft launcher", but since it is not mentioned as such in the Kimble blueprints I'd like to think that the aft launcher was a post-TMP addition to keep up with the Klingon design.
It is extremely logical to assume that various kinds of scientific probes, intel probes (drones?), and photon torpedoes would share many common components. (guidance systems, power systems, propulsion systems, and even built-in tracking systems... why not?)
I concur. The fact that a casket (!) looks like a photon torpedo or fits into the casing suggests a mass-produced (= cheap) "photon tube" for various applications. Since it's fair to assume that probes and drones require similar guidance and scanning components like a photon torpedo (which a casket doesn't) I have no doubt that this is what we are looking at (in the red TWOK torpedo bay scene
If we assume that the vertical power tube seen in TMP extends upward toward the saucer (should we be assuming that?), why do we not see it in the "torpedo bay" scenes?
I think we should be assuming that, because that's what Andrew Probert had in mind (a vertical extension of the engine core feeding the impulse deflection crystal) and because there is the same engine core panelling on the dorsal and equally on the warp nacelle pylons (with the power tubes below the panels).
On a 305 m long TMP Enterprise
the length of the TWOK torpedo bay's Section 2 would probably leave no room for the vertical core but on a 355 m long ship that might be an option I'm currently trying to visualize.
P.S. I think the "flight control room" at the stern would also be useful as control room for the tractor beam, when they want to bring larger objects aboard. Like I said, exclusively designed as a flight control room, I still think it looks a bit redundant, however if this room could also serve for other tasks it would make full sense, IMHO.