I'm pretty sure I have gotten other stuff from the UFOs in YetMoreUFOs. Either way, if it is not there, it is still possible to create new maps that have the components in a UFO the shape of a large scout (or other shapes should you be so inclined).
Well that would not be the problem, the maps are in there and could be edited easily, and yes you are right you can get a few things from those ufos. But Alien Food is not on them, can only be retrieved from Harvesters or Supply Ships.
And the Alien Reproduction only exists in the UBASE2.MCD as a asigned item. It is possible to use MCD patch to make something else recoverable as those of course, or pull in the UBASE2.MCD and place tiles acordingly.
If Hobbes can script a whole story with his first mission against the MJ12, surely one can script a mission with different UFOs. In fact, just define new UFO types like the fighter is defined in Solar's new UFOs. Call them STR_REPRO_SCOUT and STR_FOOD_SCOUT or something. Then in a new mission STR_FIRST_CONTACT, which is done by sectoids, in the list the waves make sure you add at least one STR_REPRO_SCOUT and a STR_FOOD_SCOUT.
Hobbes was only able to do this, because the first mission in the game (which is the first mission on the mission list) and the first race in raceweights of those mission is being picked for this mission to occur 100% and ahppens to be in the starting region of the player first base.
Hobbes also had some Problems because one of his testplayers missed a few of those ufos and could not start the plot for laser weapons. Which also could happen with the proposal you made.
The Alien Base is in this regard much saver, i tuned the timings so that even if you shoot down a few scouts the mission itself will not be canceled and you get the base. It is there then and can be attacked by the player, when he feels ready or when he is running out of researchable topics.
The first mission of the month would then be a "First Contact" mission, with fancier UFOs than will ever be encountered again. You can also add a "command scout" which has a a special crew with the alien dataslate on the leader.
My actual plan was to do not let the Alien Data Slate be in the base, but have another mission, were you need fight a human organization and one of the recoverables would be the Alien Data Slate.
I'm not saying it would be easy.. It is likely a fair bit of work and not something I have done myself. but defining new missions is not a new thing, the MiB and Hybrids both have entirely new missions, which have nothing to do with the vanilla ones.
The problem is not with getting the missions to work, but to make sure they occur. Since so far only one mission can be set to what you want to 100%, we have limitations, which will obviously change with missionscripting which is needed for tftd.
Then fancy things will happen