More types of field grow-able crops are in the pipeline, how far away who knows, but I think that when we get that next batch of them it would be a good time to change something about how we get seed from certain crops. Currently 2 crops are seed crops (cereal and corn) in which what we are harvesting IS the seed, another cotton is by nature always grown to the point where seeds are mature and the 'bolls' open and we get our seed by separating them, these are fine as is. Likewise potted plants are essentially reproducing by mitosis
But cabbage is all wrong, currently we get several 'heads' of cabbage and a seed stalk which dries to become seeds. Anyone who has ever grown a cabbage or any member of the Brassica family of vegetables know these plants bolt to produce their seed, and a bolted plant is inedible. This is in fact how MOST vegetables work, we harvest and eat them before they go to seed, many things (like onions and carrots) are even bi-annual, it takes 2 years to produce seed but we harvest after just 1 year.
This means that their is a distinct difference in growing for seed or growing for food which effects the market for seed, for one thing real plants produce vastly more seed then is necessary to replace the original planting, plants tend toward hyper-fecundity, even in primitive colonial agriculture we would expect a crop that has gone to seed to produce x10 the seed needed to replant itself. So I propose that cabbage (and all the appropriate vegetables to be added at a later date) basically get another growth phase that takes and additional 2 days perhaps and when it is harvested in that stage it produces only seed stalks, in the prior phase it produces just edible cabbage. Other variations are possible, tobacco for example has to be 'topped' in which the growing tip is cut off early in production to get full size leaves but this prevents any flowers or seeds from developing.
The point is that were not locked into a paradigm of 'grow to last stage and get your produce AND the seed to replant with'. Farmers should be selectively letting some fields go to seed to produce the seed they need to replant the whole operation, or some farmers might choose to grow all seed if they are rapidly expanding cultivation or are selling seed from a particularly well developed line.
Now I did NOT say 'high purity' seed for a reason, purity on seeds has always sucked (even back to Haven) it's a linear grind without any choices along the way. When we had 4 elements to purity their was a little choice in which of the 4 grind paths you were going to go down, but their is zero re-playability to that and we know purity is getting simplified. Worse of all purity doesn't have any interaction with the other mechanics of farming and field influence/fertilizer, what would be a lot more interesting is if seed has Plenty/Speed/Influence/Upkeep modifiers on it that are additive with the fields values when you plant it. The next generation of seed will migrate towards the field values so if you pump a lot of Plenty boosting fertilizer into the field the seed gradually gains high plenty too and becomes adapted to your needs. Stock&Cultivars proficiency probably needs to come in to soft-cap the whole thing somehow so elite farmers can grow and sustain a better seed too, but here you have a lot more interesting seed saving process that is more unique to you and your farming needs.