Why would undocumented people be considered for Congressional districting? They can’t vote so they are not represented by definition.
The Constitution says it should be based on the census, excluding only “Indians not taxed.”
Children, disenfranchised felons, and lawful resident aliens have always been included in apportionment and redistricting and cannot vote. Trump did not want to exclude any of these groups, only unlawful aliens.
Another wrinkle with his plan is the line between illegal and legal can be blurred. For example, successful DREAMERS did not break the law when they entered as minors, and have specific authorization to both work and remain in the USA by the federal government. They cannot be deported unless they commit a crime and can work here legally, so they are in the same position as a lawful permanent resident, except that they cannot leave the USA and then return. This legal status is pretty close to what a huge number of unnaturalized immigrants were in in the 1790s, and such people were included in censuses and apportionments.
