Yankes, please consider below features:
1) object like crafts or bases displayed on geoscape can have custom sprite, also size other then 5x5 pixels. Also different one in case hyperwave decoder is used (unknown ship / known ship), maybe even different sprite based on current ship status.
2) crafts can have optional weight limit, that could limit how much items weight can carry. This is opossite to number of items in original game. This could lilmit items that can be take for battle but also items salvaged from battle (like elerium).
3) damage inflicted to unit can be displayed as number on the top of the unit (like in many RTS games)
4) base defence buildings have N shots not just one. This could be used for cannons that fire many Times with minimal hit Chance.
5) damage taken to alien craft durig base assult should define number of aliens that will die in turn 1 of the battle.
6) alien intelligence can be splitted into two variables:
Alien will remember any soldier he spots in his field off view for N turns where N = intelligence, other aliens are not aware of these soldiers
Alien will make other aliens remember any soldier he spots in his field of view for K turns where K = group intelligence (new alien stat)
Alien will pass his memory of soldiers to any other alien that is with his field of view for M turns, where M = telepathy (new alien stat, optional, very complex to implement but could be helpfull to create chain of memory strategy for aliens, so xcom can pass grenades and aliens could pass positions of xcom soldiers that way)
So IQ = 5 and Group IQ = 1, means that alien will remember spotted soldier for 5 turns + he will make other aliens remember them for additional 1 turn
Using this engine we could implement standard behavior from X-COM but also bring much more for mods.
More here
https://github.com/Bladum/OpenXcom/commits/masterThanks
Tom