Buildings that can upgrade units

Dunno if there's a similar request (I looked and couldn't find one), so, sorry in advance. And no, this isn't Generals-style upgrades or researches (which do exist).

Anyways, I'd really like to see the ability to have a building that can upgrade infantry and vehicles (Rather, they go in, and come out as a different unit). Rather than having the tags on the buildings though, I think it'd be better for (most of) the tags to be on the units.

Something like:

[UnitType]>Upgrade1Building=[BuildingType]
[UnitType]>Upgrade1To=[UnitType]
[UnitType]>Upgrade1Cost=[Cost]

Where "1" can be 1, 2, 3, etc to allow a unit to have multiple upgrade paths

To tie in with issue 609 (Researches), it could also be beneficial to need another building and/or something researched first to send the unit into the upgrade structure.

[UnitType]>UpgradePrerequisite=[Building or Research]

This could be a nice way to allow pre-existing units to still be upgraded without having to do a ridiculous amount of coding in order to have units already on the field able to get upgrades. It'd also allow for the creation of something like a cyborg assimilation facility, where you can send certain infantry into a building and they come out as a cyborg. Or you could just have a way of simply upgrading units (and because the building and etc is defined by the unit, you could have multiple upgrade paths for units).

And if it's not too hard, it'd be really nice to have the ability for the unit's cameo appear when you select the building, similar to the RA1 spy logic. Only, it should also have a building time, with the usual indicator that you'd normally see on the sidebar when you build/train a unit.

Something like:

[UnitType]>InstantUpgrade=yes/no

For the sake of aesthetics, I think it should count as an "occupied" building, incase any modders want to give the upgrade structure a different look when it's upgrading a unit.

One more little addition that'd be nifty would be a tag that would allow an upgraded unit to retain or not retain its veterancy upon being upgraded. Something like:

[UnitType]>UpgradeRetainVeterancy=yes/no

Obviously this would take a bit of work to implement, but I think it'd REALLY benefit the modding community, and give a nice solution to the problem of upgrading units already built (you could easily, with this system, send a unit in and it can be the same as the units you'd get with research upgrades).

Again, sorry if this has been requested already- I couldn't find something like this already requested (Closest to this would be 179, the ability to have units change to another unit upon being elite, so you could have an armory do this... but that wouldn't offer near the customization).