it seems that all uboot.bin in 187B Firmwares (c180 bt) Android Auto/Carplay Firmwares are the same, maybe that caused soft brick on 5515 c210 bt firmware. Crngiar said that uboot.bin was edited in 5515 to accept 187B Firmware (512mb RAM) because 5515 was designed for 187E/C (1gb RAM). Maybe uboot.bin and vipimage.bin are stored in bootloader, the other files are in userland (file system).
it seems that welcome splash screen can be replaced by other Png included in the .tar file (GTD, GTI etc png), but renaming files maybe will cause .tar file integrity fail? did someone have tried this?