For sure there will definitely need to be more towers, as they will keep the game more interesting. I'd like there to be some kind of rock paper scissors balance of abilities for these towers. Mobile units is an interesting concept too, you mean such as factories that produce units that can fly away from your base?
I'm glad to hear your enthusiasm, I will for sure be developing this further. I assume you'd be interested in beta testing?
I will be posting updates about it on Discord and Twitter, and I've gone ahead and set up a Gamejolt page for it here! But first I must complete my current project, which was an entry for a different Jam.