Thanks for your detailed reply.
There are various ways for games to deal with the replays, keep in mind ren'py has been around for well over 10 years. I'm not denying that there are some better ways to deal with some things but we learn and improve constantly.
Of course I understand that Ren'Py is around for a long time, and I'm not telling you to copy it 100%. Just saying that when something becomes somewhat a "standard", then for the user's comfort, it should be applied. To caricature, it's like when someone had the idea to add a second button to the mouses, then everybody used it for contextual menus and other things, because it's practical, even if their competition does it too. Someone deciding to create an app and replace right click with F8 just to be different would not be liked
Also we have a unique feature which i don't think i have seen anywhere in any game (unless a more recent one has added it), called "Last choice" meaning every single choice in the game creates a save point within your playthrough so that you can always jump backwards as far as you want all the way back to the start. However mind you this is like loading back and back so you wont be able to go forward again, unless you save first, and then lets say last choice 6 times and then save that as a separate path. We try to make most choices very obvious to what our intent is with them. Again we've stated many times that we don't really punish players by including more, many choices are based on having less action with a woman you are not interested in, but not all choices are like this.
It's a good thing that it exists, and to be honest I didn't think about using it, because when I play, I usually do one path, and only wonder about other paths when I check replays. Or if I choose one path and I don't like it, I go back, but just one time.
Also, some people might enjoy this feature, but I don't have the patience for it and I'm probably not the only one. Loading 6 times (or more) to go back to a choice is a pain compared to just check what you missed in the replay's list of scenes.
And I think the heart of the problem is the frustration of seeing greyed stuff you can't get access to in the replay scenes list, even if you played the update till the end. I don't see a justification for it. It's not a type of game designed for hardcore gamers where you can enjoy replaying the same thing several times to find secrets and achievements.
Personnally I just think once the game detected that you finished an update, all paths should be unlocked for replays, even with some symbol added next to the scenes you didn't see in the first run. This way no frustration, no waste of time for the players.
There shouldnt be a difference between space and leftclick and all the other alternatives (there's like 5 different ways to go back and forth in dialogue), they should all be treated the same as they are in the same parts of the code however it might be missed somewhere. This is not something I have noticed myself as i have used spacebar or other alternative hotkeys like scrolling and whatnot. Might just be something with the spacebar mapping in one place of the code. We've probably listened more to UI feedback and improvements than any other dev that i can recall. We've added and changed so many things over the development for the better. The only thing we've had to remove unfortunately was the typewriter effect and we havent put that back in due to some issues with the new dialogue system for global translation support and new markup language, but it will come back one day. Noone has said a single word about it so, i guess it wasn't as big of a loss as I thought it would be. We're not trying to be ren'py though and i see feedback here complaining that it doesnt work more like renpy without going more into detail. One big detail is the save setup, but people have a bad habit of saving on every choice in the game in Ren'py, while here you can always go back in your choices automatically. I don't think that ren'py is good in every aspect either. The goal is the best VN experience one day, that's what drives me as the engine dev.
/A
I'll check exactly when the spacebar thing happens next time I try replay and tell you.