Another decade+ G15 user here. I've been tapping my foot waiting for Logitech to make another keyboard as perfect as the G15 but with modern features (how about a USB type C hub with a few 3.0 type A ports?). This is a huge step in the right direction after a few keyboard that do not belong outside a teenager's bedroom, but it's not "the one". For multiplayer gaming, having the name of the person speaking show up on my G15 LCD is a feature that I can't live without. I've been in the market for a new keyboard for maybe 5 years now, but instead last year I just reconditioned my G15 again.
By the way, while the new Logitech app that provides the ability to use your smart phone somewhat like a G15 screen is pretty nifty, frankly I need my phone for other things, and don't want to hassle with plugging/unplugging it so that having the screen on constantly doesn't drain the battery. Plus, my phone is too big to try to situate under the monitor.
Per-key RGB LED lighting — just stop. It's great to have a few color options, or if you want to be extra fancy just a hue/saturation slider to set the backlight color for the whole keyboard to the exact color desired. Beyond that, I don't want it. I'm not going to be taking my keyboard raving with me. I'm not looking at my keyboard while I type unless I'm looking for a key that I seldom press. Rainbows are pretty when they're in the sky, but I'd really prefer not to see them anywhere else. Ever.
Lastly, wrist rests are not optional for me. I have no idea how a $50+ gaming keyboard gets released without a wrist rest, much less a $150+. Mind blown.