In the world of arts funding, pretty much everything -- orchestral seats, chairs, drinking fountains, seats, curtains, rest rooms -- is now a "donor opportunity." Given this situation, it looks like sponsoring individual dancers is the new reality ... at least for companies with a donor base that can support it.
If I recall correctly, ABT did not start off with sponsorship for all the principals. That happened only with time, as is probably the goal at SF.
One serious drawback to this would be if the patron begin to act as though the individual dancer actually owes them some sort of compensatory service. Or, if the sponsorship is contingent on hiring or promoting a protege who might or might not qualify otherwise. There's a reference in the NY Times story linked by abatt to a board member of Colorado Ballet who went to China scouting for dancers and who returned with an offer to pay a year's salary and expenses for two dancers he liked. One dancer worked out; the other (too tall) did not. This sets a bad precedent. I also wonder about those rare sponsored corps dancers. It would be unfortunate if the sponsor turned out to be a doting relative with deep pockets, or something like that.