Iron Grinders: No comment - wasn't directly involved in acquisition of one this rev. Support emulation of vanilla costs, or as close to equivalent as possible.
Portals: Happy with portal density this rev. Would be open to trying something like 4 hidden/claimable portals + spawn to start, then allowing portals for /places after 2? weeks into rev or when livemap revealed. Restrict minimum distance between portals. Danger of killing rail even further, but eh.
Nether: Custom nether that feels more like vanilla - more vertical, cavernous, dangerous.
Map Generation: Size is good, though I'm always up for a bigger map when technically feasible. Big YAS to second overworld appearing mid rev with extreme difficulty/hostility even for people fully kitted out. Custom biomes/terrains were great - particularly enamored with overhanging cliffs and the desert-mesa-plateaus. Large sandstone deposits in desert were a godsend. Suggest diversifying actual biome type - e.g. very little mesa biome proper even in mesa-looking terrain. Land:water ratio was fine. Prefer custom terrain to worldpainter (though throwing some WP/WE terrain on top could be interesting) and prefer WP to vanilla.
Ore Distribution: Was neat to find ores at weird y levels. Seemed to be harder to mine for materials in bulk. I missed the sponge recipe lol.
MapWorld: Gib FAWE
Misc: No to flatworld on P - that niche is nicely filled by C - perhaps can ask cadmins to carry testworlds forward?
Spawn: Multidirectional exits from the start, food was fine, size was fine for me but could be problematic for weaker computers. Odd/misc ideas: have a spawn not at the center of the map, have spawn move around the map each week (flying spawn would work best for this), have rail station within spawn itself. Themes: Ruins of a previous P spawn/build, megalomaniacal evil lair of doom, walking nuclear castle, the bovine digestive system, any single color (e.g. orange), an art nouveau or art deco style art museum, giant subterranean cavern with stalactite buildings inside (actually no, don't do this - I have a patent pending on the concept since 2011).
Special Spawners: Maybe try alternate spawners in premade protected "dungeons" with higher rates of spawns, and lower spawn rates for grinder-buildable spawners? No-danger grinding would still be an option, but underpowered compared to actually fighting the mobs in question. Custom structure spawners were nice.
Events: Hunts are cool. Holidays: Halloween, Thanksgiving, Christahanukkwanzaa, New Year's are the standards. Other possibilities include Earth Day, Labor Day, Mother's/Father's Day.