Just a few things that need more thought:
-What happens if you fall down. should there be some sort of playersensitive portal that sends you back to the correct team's spawn? Or do you play it like a deathmatch, either capture the flag or destroy the enemy team entirely.
-If the enemy gets your flag to their side, you can not let them fall anymore, only if they fall in a hole of their own team, they fail.
-How do you intend to register who captured the flag, for now you can't see who has the flag, and when the flag is taken, anyone could just plant it in the homebase claiming they scored.
-If there was any way to get armours to work in classic i'd say give the one with the flag a nice hat with the enemy colour so everyone can see it clearly. Maybe give all teammembers pieces of chestarmour so you can easily see who is in your team.
-As for the no destroying around flags, It's useless since you will have to bring the enemy flag back to your own too, so you won't be able to reach it if you do this. Maybe more fun to let them find out for themselves instead of prohibiting it
-A timer for the removed floorblocks could be useful, as even with 2 players, a reasonably big field is untraversable within a minute. Having the holes stay for 10 seconds should be enough for everyone to fall in in the heat of battle.