As a Gold I've checked in early quite a few times. Typically no more than 2 hours early. No issue as long as the room is ready. Never have been proposed a fee. I can think of about 2 times where I had to wait for my room.

I have also on Priceline reservations checked into a couple of Hiltons early (not as a Gold)... I am really under the impression most properties are glad to do early check in if they have a room ready. To propose a fee is just a money grab and to do it to someone who is a Diamond is certainly low. I kind of get it for Golds given how easy it is to obtain Gold... let's face it...

I tried to do early check in as an IHG Platinum at an Intercon last month and at 12:45 PM was processed then right as the process was done the clerk says "I have pre-checked you in and we will text you when your room is ready." I asked if anything was available now. I was told "we do not guarantee check in until 3 PM." Okay, thank you. Text arrived promptly at 3 PM. I am a little conflicted as to whether or not a room was really unavailable at 12:45 or not.

I think Hyatt with its specific benefit-level promises regarding check in/out is better for this sort of thing.