Comment 1 for bug 1239004

One alternative is to only encrypt user-home directory, then your personal files are protected and will be decrypted upon login from lightdm, which does support touch screens.

Ideally plymouth would support touch-screen input.

Or we somehow include touch screen support into initramfs and/or alternative input methods.
E.g. using hardware keys that are present, e.g. "volume up/down".

Or create a small unencrypted install that lets you unlock/mount encrypted root and chroot into that....