That tank minigame was the most enduring part of Tyrian, for me.
Agreed on not making this a Kickstarter stretch goal, because that would be really off of the beaten track. Not to mention I wouldn't invest nearly that much time and energy into making this.
I suppose the reason for asking about reactions to this as a minor easter egg sort of thing is that at this point I'd be using the funds from other people, not myself, to be self-indulgent. Aka, I could see some backers saying "you used the money I kickstarted for WHAT??" So obviously it would have to be small in scope and just a fun little thingie, and if it gets any larger then it's on my own personal time.
If it were to get too large past a certain point I'd just want to spin it off into its own game anyhow, and a game in that genre is something I want to do anyway, at some point. So there's an inherent scope limit here, which is nice.
The reason for not making it so you can control one of your actual ships and destroy actual enemy ships is that then this can cease to be a strategy game by accident. Suddenly skill at this little minigame might become accidentally important for "optimal play." That... would be very very bad.