Currently there is a hard set and specific list of unit types available. Structure, mobile, artillery, land, air, amphibious, ect... Would be nice if we put in a new one, unit_retarded, and specified a buildable types as "unit_retarded", that we could get the game to recognize the unit type and link it to the unit requesting it to list in build. The issue is, making new types of units, you have no way to specify a factory to build it, without being coy and giving it opposites together or a really long string of [and/or and and/or or and/or] situations that specify what you need without giving anything else it, like buildable_type: mobile and stationary or land Requested for maximum addability to game, such as factions.
Definitely agree. The only tricky part is that the UNITTYPE values actually correspond to a binary flag, so at present custom ones can't be easily allowed by uber. https://forums.uberent.com/threads/pa-client-api-requests.57785/page-2#post-948571
Units by name being allowed in the buildable list is acceptable. Also acceptable, is just to make a sufficient list of "generic" unit types. Like "type_1"-"type_20".