When IBM starts to say they are going to deprecate something in mainframe, they will deprecate it in probably 10-12 years time. There will be 3 versions in between and each version will have a much better migration path. If a corporate don't want to take risk, they will be mostly the last ones to migrate, after confirming &consulting all the IBM tech champions, they would start the migration process which would last a year, before they install the new version.