All your ideas are amazing Aria! I especially like these ideas:
~Swaying trees
~Traveling/swimming Speeds
~Thunder+Lighting
~Sound Effects
~AFK Icon
~Multiple Markings
lol i can't tell you how many times someone has sat there talking to me and having like a serious legit conversation while i wasn't even there, or i was frozen lmao. All the things you've realized about sound effects and the water have been on my mind too. Or how loud the water sound is when you not even swimming? When you just standing in the water it's like "WOOOSH WOOOSH WOOOSH WOOOSH" xD Idk maybe it's just me. And there also have been many times where ive wanted more than one marking on my charries... so i love your ideas and i hope a lot of these get taken into consideration!