My suggestion: I think the balance is off between the two modes, especially vs what is likely able to fit into one GSOC. I suspect if you were to aim for the short CTF you'd hit a wall on stuff like "More powerful guns" - you could easily spend an entire month on that, another entire month on potions, and another on towers. Let alone marketplace or observer mode. Getting those kinds of things working really well in multiplayer can be
hard.
I think you could go for just those three as primary goals, shift marketplace and resource stuff into the bigger CTF, which becomes more like a Battleground. At 15 minutes expected duration (if goal is 5 points that's
three minutes per round or less) the idea of navigating a UI to purchase things sounds like it would be potentially disruptive. Less so at an hour.
Maybe if it was something like picking a class on the lobby platform before spawning into battle (just make multiple team selection blocks and have it cost some resource to pick others). That could also really be enough slowdown punishment for death - just having to navigate the spawn platform, rather than spend nearly 10% of a game waiting because you died once.
You could still write up a bunch of the extras as stretch goals. But start trying to detail exactly
which weapons and potions (I'd go for powerups, really, maybe even spawn them directly into the world, maybe on obstacles) you'd want to include. Then think about how they'd be implemented. The added detail might help get a better feel for just how long it would take to implement.
For the towers two big questions to consider: do you make them spawn as part of the arena (my recommendation), or do you add the complexity of having players somehow place them, and acquire them in the first place? And what logic will they use? If you can drop in the "towers" from GooeysDefence and just tweak them to hit a player then be done then that's one benefit and that might not take a month on its own. But ask
@jellysnake how long it can take to get that sort of thing working well
I'd also still go for weapons and powerups that focus on movement instead of power (although you could probably get a powerup that temporarily supercharges how much a defense tower would push a player). We're not playing Counterstrike here after all - it is a dark fantasy setting in a magical place. You don't need to upgrade into higher caliber bullets and treat players like bullet sponges. You've got
magic wands
Remember: The current L&S CTF setup? That took
three months to get right.
