We plan to deprecate and remove xblock.fragment and direct id_generator parameters in xblock.runtime.Runtime. Both have been explicitly marked as deprecated for years and have direct replacements. We are targeting removal after 2020-01-24.
Please read https://openedx.atlassian.net/browse/DEPR-59 for more information and to post any questions/comments. The proposed deadline for comments before acceptance is 2020-01-13.