My recommendations in the previous article were based on the assumption that I would be following my standard rule of not imposing level limits on demi-human characters, but perhaps there is a way of preserving level limits in such a way that it does not discriminate against them. Therefore:
Any character, human or demi-human, who has but a single class, has no limit to the level he or she may achieve (and any character can choose any class).
Any character, human or demi-human, who is multi-classed, is limited to the 9th level of experience in any class.
In summary, any character can be multi-classed regardless of species, but will have the same level limits. Any character can be single-classed in any class and will have no level limit.
This does not mean that all classes are equally common to all species. Player characters are exceptional. Non-player characters may very well conform more closely to the D&D standard.