Not sure if there are any Final Fantasy XII fans here but in that game there is a machanic in place called the “Gambit system”. Essentially you are able to trigger your different party members to do things using conditional statements. So whenever one member gets below a certain amount of health you can make your healer automatically heal them.
I think it would be a great implementation to add this concept to defense teams. This would create an opportunity for players to pass on their strategies to their defense team and it would make the experience of the opposing team less monotonous and more challenging with variance.
We could make the computer favor a specific gem color initially to charge whatever troop we wanted to charge first. We could prevent our gem converters from converting unless there is a 4 gem match after conversion. We could program our summoners to hold until there was an open spot. We could overall change the order of casting in situations where multiple troops are charged and order makes a difference. We could skip skulls in cases where we are entangled and charging would be the better option. We could pre-designate targets instead of having the computer choose.
I know this is a huge feature with way too many possibilities and it will likely never be implemented but one can dream!