I used this thread to change my Vero 4K+ splash screen. I initially tried a 1080p one, but it looked horrible. Mine displays at 720p so I resized it and it looks much better. There isn’t a lot of image processing at this point I guess.
On that note, does OSMC have a collection of images that you could share for splash screens? I can’t remember where I found mine, but it is a nice blue gradient with OSMC on it.