Although, Delete route into Expired SCD 2 does work as expected

I'm afraid I don't understand where the problem is.
Your first paragraph says that you "always need to use the New SCD2" output... and that this was a fix in v1.5 - which I understand means that "it works". Your second paragraph says that choosing to route those rows to "New" (not "New SCD2") isn't working in 1.4, but is fixed in 1.5.
What's broken, exactly?

Ok, when I clicked "Route rows to NEW (behave as 1.4) checkbox" I expected SCD1 and SCD2 updates to work when being applied at the same time.

For example:

Existing Dimension:
key, ID, numberSCD1, numberSCD2, currentFlag,
1, 1, 1, 1, 1,

Update in Source for both numberSCD1 and numberSCD2 from 1->2, gives the following results - which shows the NEW SCD 2 record is not coming through into the NEW path when both a SCD1 and SCD2 is being performed:

key, ID, numberSCD1, numberSCD2, currentFlag,
1, 1, 1, 1, 0,

So, the bug that is in v1.4 is still present in v1.5 if you re-route the NEW SCD2 into the NEW path.

Hope that makes more sense.

This means you always have to use NEW SCD2 for those updates that consist of both a SCD1 and SCD2 update in the Source.

Found this one...

great, is there a new version coming soon on this?