Any word about adding quicksave / manual save during main quest?

Wasn't giving you a "why" for it... I mentioned it because it might have been that your recollection was incorrect as far as ME1 and ME2 having a quick save option... or it might have been a difference between PC and console play.

The industry trend seems to be moving away from giving the players saving options... which is not a good thing IMO.  ME3 did it right... other games should follow that lead, IMHO.

Admittedly, it is more of an issue on consoles.  Mass Effect 1 had 10 slots for manual saves, no quick save.  You could however start another game with a different Shepard and have as many different Shepard's has your disk space would allow.  RotTR does not allow for manual saves.  It saves at checkpoints.  There are only 3 slots for 3 different games under one profile and no way that I've found to have more.  Assassin's Creed IV does 2 autosaves, alternating overwriting.  You can have up to 2 or 3 different Edwards (games in progress under one profile).  TW3 does not allow you to have 2 different Geralts on the go at the same time.  Starting a new game will automatically delete/overwrite the old one.  There are 7 manual save slots, and, I believe, 3 autosave slots, and 3 or 4 checkpoint save slots.  The autosaves and checkpoint saves will overwrite automatically... so you have a maximum of 7 save slots that the player controls.  I would like to see the industry trend on the consoles move towards allowing as many options for saving as the PC's seem to get.  I don't see a good reason for such heavy restrictions... particularly since the consoles today are more powerful and have more memory and drive space than the old gen ones.  However, as best I can tell, they seem to be moving in the direction of just forcing the autosaves and allowing nothing else.  I don't know if it's console thinking that prompted Bioware to go this route with ME:A.  I can only hope they rethink that and allow for more manual saving whenever the player desires in the future.

On the Xbox 360 disk cases I have, none of the Mass Effect Trilogy games were actually "labeled" RPG.

Was this a console thing? Because on PC you could save anywhere that wasn't a cutscene, conversation, or combat in any mission in ME2 and ME3, DLC, priority, or otherwise.

No PC, I havent paid attention to any changes, so maybe they changed it.
No save during a priority mision was added with ME2 DLCs, I can not remember Firewalker and Overlord, but Lair of the Shadow Broker and Arrival had it, I could no longer save whenever I wanted and not just because it was locked due to combat or cutscene
ME3 had this during priority missions, though I can not say how bad it was, maybe it was limited to certain phases during the missions. I never saved ME2 and 3 that much, as the games were extremely stable, pretty much bug free and the combat easy, but I remember the typical message "you can not save during priority mission" now and then.
MEA "save feature" is just the next logical step. Just have no idea why it is there, to me it adds nothing but frustration to replay a particular "phase" (which is not just one room) over and over and over again until I master it.

Err;
In the Trilogy, saving was not possible when enemies were around, in cutscenes, or during conversations,  and also not in elevators or doors. ME2 also didn't allow to save when in the Hammerhead. (Haven't played Arrival, so I cannot comment on that.) ME3 did not allow to save during "Priority: Earth", I cannot remember if that was during the hole mission, or just after arriving at the FOB.
Otherwise manual and quicksaves were always possible, with additional autosaves at certain points. (PC here, too)
Meanwhile MEA does not have quicksaves and does not allow manual saves at the same instances as the trilogy (you can save in the nomad, but not load those ).
But it also prevents manual saves just randomly in between. E.g., I'm not allowed to save in Prodromos, except in the medbay,  R&D,  or just outside of where the merchant is. WTF

I'm almost positive I could save on the Shadow Broker's ship. The chase, no, but that was sort of an 'event'.

ME3 priority missions absolutely allowed quicksave as long as something wasn't happening (including in between enemy waves, because that still counts as being in the same combat event). But I could save during priority Earth, and I definitely could in priority Tuchanka, because I was using quicksaves when modding it.