Something I noticed is that when playing on a alpha generator world and using old mob spawning, monsters don't spawn. When turned off, no animals spawn (I didn't test it with beta worlds). Why is that?
I just tested it out using the Alpha generator and the Alpha 1.1.2_01 preset and it seemed to work fine for me. Both animals and monsters spawned fine for me, perhaps just changing the setting a little through back to the Alpha 1.2.0 setting would fix it? Although with this I did discover that squid still spawned despite using the Alpha 1.2.0 mob spawning setting so I'll have to figure that one out.
Something I thought about was having the ssp mod for newer minecraft versions because server lag is something I really hate about the newer versions starting at 1.3 and I know lots of other people are annoyed by it too (especially because creepers explode way faster because of it), is that possible without lots of work? I don't really know anything about modding lol.. I (and I think a lot of other people) would love to have it when playing newer vanilla (or modded) versions of minecraft.
It would be neat to port SSP to newer versions, but it would most likely need an entire rewrite since a ton has changed since 2013. Even then I would need to learn more about Java before I'd take it on unless someone else decided to do it. And also it would most likely be incompatible with Forge as Exalm originally stated due to how Forge works with the game. And it probably wouldn't work as a mod like you'd install a modern mod since, I think at least, Forge acts as a between layer for Minecraft and mods, allowing access to parts of Minecraft but not all of it. Now maybe it would be possible to create a specialty version of Forge which would bring back SSP, but I really have no clue and it would most likely be a very niche thing.
So for now it'll remain a 1.6.4 only mod, but I do hope to one day try porting/remaking the OldDays mod for newer versions, but I once again still need to learn more about Java.
Sorry, but it's not possible since the Joypad mod requires Forge and OldDays doesn't not and will never support Forge, at least the 1.6.4 version won't. If a port ever does comes for new versions of Minecraft, theoretically it should since it probably would be using Forge.