Thank you everybody for your attention to this problem.
Based on previous comments, let me rephrase its description to:
Ubuntu text mode installer should ask the target location of the boot loader. It does not require any automatic mappings between Linux and GRUB devices, just a list of available drives and a way to specify one of them manually (like it is already done in Expert installation mode). This feature would be especially important for Ubuntu Server, as it does not have a GUI installer, where this feature is available by pressing Advanced button
Thank you everybody for your attention to this problem.
Based on previous comments, let me rephrase its description to:
Ubuntu text mode installer should ask the target location of the boot loader. It does not require any automatic mappings between Linux and GRUB devices, just a list of available drives and a way to specify one of them manually (like it is already done in Expert installation mode). This feature would be especially important for Ubuntu Server, as it does not have a GUI installer, where this feature is available by pressing Advanced button