Now that 1.20.5 is out, I'd say it's time to do some proper ports.

• 1.20.6: Big changes to datapack format, last minor version before 1.21
• 1.20.4: Big stable, long running version
• 1.19.4: Latest version of 1.19.4 and still decently popular
• 1.19.2: Most popular version of 1.19
• 1.18.2: Latest, most popular 1.18 version
• No earlier versions planned

Concerns:
Don't ship compat entries for mods that don't exist in a given version.