Since I haven’t taken any subject tests yet, I planned on just submitting my ACT score since it would be accepted in lieu of 2 subject tests; however, now the subject tests are recommended for SAT and ACT. Despite Penn’s website saying that one won’t be at a disadvantage for not sending them, do you think I should take subject tests and send them with my ACT score? Or should just the ACT score be sufficient? This sudden change really threw me for a loop 
Whatever the requirements are is what is “sufficient,” but I would send SAT II scores regardless (if a college recommends something, that means it’s best to send it). Plus they help demonstrate your mastery of a specific subject, which can’t hurt.
If you can take one or two subject tests without too much difficulty, it would probably be better.
What classes did you take junior year, and which school at Penn interests you?
I took AP Bio, so I could probably take the bio subject test. I’ll try literature since it doesn’t seem as extensive to prepare for. If I take subject tests, I have to take them in November. I also plan on applying early decision to the College of Arts and Sciences. Would it be too risky to send my scores without even knowing them? I feel like that’s better than not sending them though.
I would try a couple practice subject tests and see how you do. If you do okay, I would just have them sent.
I think there will be students without them due to the last minute change. It should be helpful to you if you can get them in.
In my opinion not sending subject tests ca hurt your chances, no matter what the website says. If you read their announcement it says at they strongly encourage subject tests because based in their research, they have determined that subject tests are very good predictors for college performance. Given how competitive admission is i would recommend being in the safe side and taking the subject tests.
Thank you both for your help!!