Why not? It wouldn't unbalance herb tables because if you plan to have a tobacco plantation you'll have to invest in herb tables anyway. But it'd give early and low-tech gardeners something to do with tobacco leaves while herb tables are still a pain to craft. Perhaps do the same for tea leaves and hemp buds too?
Oh, also have them halve the quality, like with WWWs. Plenty of precendent for having this extra option already in game, so again, why not?