Thoughts on a Quicksave Reminder

I love when I die in a map because I forgot to save. That's when I know the map is good.

I don't think there's anything wrong with a quicksave reminder idea, but I also doubt too many people will care about it enough to want to implement it. I could be wrong.

The way you propose it that it reminds you of saves before important events is something that would also be done on a map-by-map basis. So even if you could get some people on board, you're very unlikely to ever find it in the majority of maps.

You might be interested in checking out the dsda-doom source port, which allows you to rewind your game up to a point. It doesn't handle GZDoom-only maps so depending on your interests you might find it insufficient for normal play or mapping, but it's otherwise very full-featured. Some people also find the idea of unlimited rewind both too lenient and too tempting to use when you die, so it's not a feature for everyone.

Personally, I've gotten to the point, especially in non-slaughter maps, where I don't quick save when playing through an entire level. This gives me a challenge that I wouldn't otherwise have. If I do die, however, on my second run through I would then give myself a quick save in the room right before I died. That way I don't get frustrated when dyeing all the time. ZDoom and its child ports offer autosaves as line specials, but I don't see them implemented. Thats a great thing about older games, they offered the ability to save anywhere not just at checkpoints.

ask yourself What kind of experience are you trying to give the player?

OH I'm definitely not trying start a community trend or anything of that nature.  I primarily want to design good gameplay experiences that speak to as many people as possible regardless of experience.  Due to the nature of Dooms community and players that have been playing for 30 years to players that have been playing for 30 days, I find this to be a difficult bridge to gap in level design.  But i mainly just want to be sure im not doing anything that the larger community more or less sees as distasteful? Or not in the spirit of classic doom? I could be thinking too hard about it

You can telegraph dangerous fights with in-game indicators, such as a larger-than normal pile of dead bodies, a lot of health and ammo (a "free" soul sphere or such is an especially potent indicator), ominous architecture, the existence of a visible keycard.

Finally, some map formats have lines which can trigger an automatic autosave, although that doesn't work if the player is using a non GZDoom source port.

Not quite a fan of hand-holding in video games, so I definitely wouldn't vibe with a feature that consistently reminds you that you probably should save your game. I'd sound quite a bit old by saying this, but honestly... if I want to shape your skills and let your own instincts develop, one really shouldn't have to be "reminded" to do it, they should just have practiced through a handful of maps just enough to have a mere instinct, a.k.a a gut feeling that you should probably save. 

But, some people do prefer hand-holding, so I'm not going to shun the idea completely.

Having a map autosave when crossing a line always feels a bit immersion breaking, because the game just freezes for a fraction of a second. But telling a player through a HudMessage to save also doesn't seem great.

I think the best compromise is to trigger an autosave by picking up an item. For example Verdant Citadel uses this technique. Although I'd put those items not right in the path like Verdant Citadel does (but still clearly visible, so that they can't be overlooked), that way it'd make it harder to pick up accidentally, in case the player doesn't want to save.

Having an interactable element to trigger saving is a good way to do this. Beyond Sunset has terminals that save and everyone you see one it's like "oh, I'll go save now". It's the player's choice to do it so you don't get the surprising lag, and it's woven into the game aesthetic in a natural fashion.