I have two suggestions
1 - Enable pay per use. I have used Cubase since the earliest versions but I am not using it as a profession and so I am not getting value for money
2 - My son uses virtual DJ software (for live DJ work). It has a feature for isolating vocals which looks and sounds very similar to the one in RX8. How about including similar in Cubase? My understanding is that its based on open source software so shouldn’t require too much development.
This exists in Spectralayers. Spectralayers One is included with Cubase, can’t remember if the vocal component is, I think it is.