Hmm... I like the idea of more exploration being useful. Maybe each flower past a certain point in progression requires a different of metamorphic stones? That way, exploration is not 100% required, but having different bases in different biomes would help. Then, later in progression, you require shimmerrock instead of metamorphic stones. Even later would require bifrost blocks, with the bifrost rod having a dragon head in the recipe.
Custom items from piglin bartering is also neat. Maybe villagers can trade "elemental catalyst", required for elemental runes, piglins can trade "seasons catalyst", for seasonal runes, and a dragon egg can serve as a "sin catalyst" for the sin runes. Of course, you'd want to be able to duplicate the dragon egg, but that's not hard. The egg would not be used up, but the other catalysts would be.
So, the progression would be:
- Overworld, T1 flowers - get the runic altar
- Overworld and Nether, T2 flowers, trading with villagers - get the marimorphis
- Overworld and Nether, T3 flowers, metamorphic stones - get terrasteel for access to elven trading
- Overworld and Nether, T4 flowers, elven materials - Prep for Gaia 1 and dragon fights (maybe blacklist the end portal from generating, making you craft one?
- All three dimensions, egg and dragon head - Gaia 2 fight
- Endgame, see below.
Endgame goals might just be the guilty mana pool, but that's not to say it'd be easy. Something on the runic altar like 8 blocks of terasteel, a dice of fate (and maybe a SS tera shatterer) sounds sufficiently grindy for a creative tablet. Then, use four of those and five blocks of gaiasteel to craft the guilty pool.