This will never be possible in cloud. Alternative solutions are being explored.
This will never be possible in cloud
Remote LDAP Integration
SIL Template Language
This functionality is not relevant in cloud
This functionality is not permitted in cloud
Workflows Conditions/ Validators
Available to the extent to which cloud allows
Workflows Post Functions
JQL Keywords vs JQL Functions
A JQL function performs an evaluation of the issue in real-time during the JQL search. This type of search is not possible in Jira Cloud and may never be possible in cloud because it is a very resource intensive way of searching. A JQL keyword is meta-data for an issue that has been evaluated and saved prior to a JQL search. This type of search will always be faster and more efficient than a traditional, functional search since the results can be indexed and it is less resource intensive.
Live Fields (screen manipulation)
Due to the limitations of the Atlassian Connect framework and the Forge framework this type of direct screen manipulation will never be possible (or permitted) in cloud. Alternative solutions using panels are being explored.
The only solution available for custom workflow conditions and validators is through the Atlassian Expressions language which has limited functionality compared to SIL.
There is not cloud API support available for all of the routines that exist in server today. There are some routines that are missing from cloud that have not been created yet although we are working on them. These actions (for the missing routines) are still supported using the REST API.