Tumblestone farming has some specifics that are unfriendly to typical farmable materials. Unlike amethyst clusters, tumblestone clusters need to be replanted. I believe making them placeable by dispenser would be reasonable. I would recommend they are placed on the block opposite the dispenser or if there is no block there, on the dispenser face from which they are exit. In survival mode, if you have a farm big enough to warrant it, you also cannot pick block on a small tumblestone bud to get more tumblestones in your hand. If it is possible, there should be a pick block priority of small tumblestone bud then tumblestone for each tumblestone type so that someone hand placing mass tumblestones doesn't have to go into their inventory between stacks. I believe the current best possible afk farm, using vanilla mechanics, is a player riding a minecart with auto-refilling hand and placing tumblestones that are broken by pistons. I believe the experience could be improved by dispenser placement or perhaps a pokemon's help in placing them in the long run. Something I don't have recommendation for currently but find both to be interesting to making a farm for and potentially confounding is the very tight hitbox changes between growth stages and their relatively short nature (compared to amethyst/nether wart). Down the line, riding a certain pokemon may put the player at the right height to afk farm them (without breaking earlier growth stages). But also I believe there is a creative solution here. That said, I still think the other additions may be warranted