I have a few ideas, you should add a third menu category, Make it bloon properties and then you could add stuff like shield bloons, lead bloons, purple bloons or camo bloons. i also think there should a secret that makes you a ddt, like if you had 100 Moab hp so you are a full Moab, then have 28 normal hp because d is the 4th letter of the alphabet, 2 d's ant and a t = 28, and you also have camo and lead, you become a DDT and as a bonus get DDT speed.
Next suggestion: I think you could make it so like through certain methods you could upgrade road items, like corrosive or Moab glue, or white hot spikes, and pls add pineapple bomb, and make its upgrade the cherry bomb pls.
Suggestion Three: This is a bit of a stretch, but maybe collab with the person/persons who made bloons fps, and make it a versus match, between the player wo fights themselves and the sentient bloon, who can use all sorts of gadgets to attack.
Suggestion four: Add more monkeys, the ones i think would work best are, buccaneer, village, and farm.
Suggestion 5: I think that you should make a custom map, and in it have a secret path that can only be unlocked by puzzles, and on the inside make some special parkour with some sort of secret or reward on the end, this is one of the ways you could unlock the things in S2.
All and all these are some suggestions but i will be happy with (Almost) anything in the coming updates.