I too think lategame is a little lack luster. The argument that only a minority of player base reaches endgame and thus subsiding the need to add lategame content is absurd. The goal of the game is to survive, not experience 'early game' then make a fatal mistake and call it a day. Adding late game content is important as it adds depth to your experience surviving the apocalypse, and keeping the player engage which also affects their decision making in the early game. But I'm not here to debate on that so here are my suggestions: (Note - Some of these ideas have already been suggested, but since I liked them I'll share them here anyway)
• Vehicle customization - Decking out your post apocalyptic vehicle to better dismember zeds during your loot runs.
• Wandering / stationary traders - Got ample of food? Trade them for ammunition or equipment.
• Zeds with unique behaviors - Some zed may have different mutations making them 'smarter' or stronger. They might scope you out for several days during the night before attacking you when your guard is down.
• Blueprints / research - These can be use to craft better base defense / improved weapons. May also be obtained through trading.
• Horde nights? - Kinda like 7days, not sure if it fits with PZ
That's all I got. They aren't the best I know but its something. Feel free to expand on them or suggest more I would like to hear yours.