The nice thing about race-classes is that they can be used to make the choice of playing a non-human race more special than in a separate race & class system. Traditionally in D&D, the choice of race in a separate race & class edition doesn't covey much more than a couple of mechanical bonuses/penalties and some roleplaying fodder. In a race-class edition, like BECMI, choosing to be an elf, for example, gives the character unique mechanics that really separate it from the human classes and make it feel more "alien". This wasn't always done to maximum effect (the dwarf is too similar to a fighter), but there are reasons to consider implementing race-classes beyond mere nostalgia.