I wouldn't put any restriction on it, personally. the author (Cliff) obviously didn't think it was important, so you shouldn't either.
The Metatype column is weird and its exclusions seem arbitrary in 6e, built on deep Shadowrun legacy ideas of which metatypes are more special than others. There are combinations where Elves and Tandorans could spend all 13 possible metatype points, just as there is a combination where humans could spend 11.