I’ve been against having day/night cycle in the microbe stage before, but this could make it work, and also would make vacuoles (more) useful.
This would tie into a really old suggested feature of turning of organelles:
I personally would like the downside of photosynthesis to be weight. This is basically @tjwhale’s idea.
Pardon me for not finding a link to the original idea, but basically in real life the downside of photosynthesis (and why animals don’t do it and why plants aren’t sentient beings running around) is that you need a lot of chloroplasts to get any sensible amount of energy. So in terms of cell stage this would be that the chloroplasts would have their mass increased like 30 times making moving basically impossible. We can’t do that now but once these other features are implemented it should work: currents moving cells, and stuff spawning even when stationary, and the cell wall being a good protection against engulfing and pili, and toxins to give immobile cells a chance.
Basically my idea is that plants should be required to be actual plants in exchange for being able to do photosynthesis.
Edit: one more idea that is also probably from tjwhale: make photosynthesis so ineffective that you need more than 70% of your organelles to do photosynthesis. To also force a player to be a plant if they want to be a plant.