Merge terms of different vocabularies

I've tested the module, but only merge terms of the same vocabulary. I'm trying to make something tha i've seen called "Taxonomy on the fly" (An old module for 4.6).

There are two vocabularies:
- 1. Solutions (Simple jerarchy)
- 2. Solutions (proposed terms) (free tag)

The user add a term as free tag in voca. 1, and the administrator send, if useful, than term to vocab. 2

I thought this module would be useful.