RDBMS -- XTTS (+incremental rman backups) -- how to do it when the source tablespaces are read only?

In my previous post, I mentioned that the method explained in MOS document " 11G - Reduce Transportable Tablespace Downtime using Cross Platform Incremental Backup (Doc ID 1389592.1)" requires the source tablespaces to be in READ-WRITE mode.

The xxtdriver.pl script which is in the core of the XTTS method powered by incremental backups, just checks if there are any tablespaces in READ ONLY or OFFLINE mode..

What if our source tablespaces is in READ ONLY mode? --> According to that note, the rule is simple -> if tablespace is read only, use traditional TTS.

Why? Because it is a requirement of the process described in Note 1389592.1.. This requirement is checked inside the xxtdriver.pl and that's why we cannot execute this XTTS(+incremental backup) method for readonly tablespaces.

I still don't understand this requirement, because there seem to be no technical impossibilities for this.

Anyways; in my opinion, Oracle wants us to use this XTTS (+incremental backup) method when it is really required..

But, there are scenarios where a read only environment is required to be migrated using XTTS (+incremental backup) method.

One of these scenarios is an active dataguard environment, and the other one is described in the following sentence->

During a migration process ; a source environment can be readonly in t0 (time 0), then can be taken in to  read-write mode in t1 (time1), and then can be taken to readonly in t3(time 3).

So far so good.

What if we want to use XTTS (+incremental backup) method for read only tablespaces?
Then, my answer is use/try the manual method.

As I already wrote this down in my previous blog post; XTTS based conversion is done using the sys.dbms_backup_restore package. 

xxtdriver.pl uses it and we can manually execute it too! 

Moreover; technically, if we use that manual method, we do *not* need to make source tablespaces read write.

In the following url, you can see how this is done manually -> https://connor-mcdonald.com/2015/06/06/cross-platform-database-migration/

Ref: https://connor-mcdonald.com

Although I haven't test it yet, I believe, we can migrate our read-only source tablespaces  using a manual XTTS(+incremental backup) as described in the blog post above. (**this should be tested )

There is one more question.. What about using a Active Dataguard environment as the source for a XTTS (+incremental backup) based migration? .. 

Well.. My answer for this question, is the same as above. I believe, it can be done.. However; it should be tested well, because Oracle clearly states that -> "It is not supported to execute this procedure against a standby or snapshot standby databases".. (**this should be tested )