IMO, "smcp" should not change figures from the U&lc text default, because small caps will most often be used in concert with U&lc.

However, for "c2sc", which is activated as part of "all small caps", then small-cap-height lining figures are appropriate. It's extremely unlikely that such a style would be used in a tabular-figure setting, so only one set of figures, proprotional and kerned (really only between 7 and 4) is necessary.