Hi,

I am in the very same place. I started the application form online but havent finished it yet because of that. Also, I thought about registering and have a registration number but that might take months. So, I am thinking of writing "do not have one" in the application field which asks for the registration number, but I am afraid my application might get refused based on that. I am right now seeking advice and information that might help proceed. I will keep you posted if I get any new information that might be useful to us. Please you do the same.
Best regards

 

The reference to it not being mandatory to complete the application form simply means that you could instead, just write a letter, as long as you give the necessary information. That is because the relevant EU law does not say you need to complete any particular form. It also means that you might find it more convenient to complete the form instead of trying to guess what they want to know and then getting your application rejected because you forgot something.

An EU national living in the UK does not NEED a registration certificate, but if you do have one, it might save you and/or your spouse having to submit other documents to support her EEA Family Permit application.
Regarding the Registration Certificate, the issuing authority is required to issue( or reject!) the Certificate within 20 days of their receipt of application, and the evidence is that they do!
For any non-EU/EEA Family Permit holder thinking of applying for residence, there does seem to be an advantage if the sponsoring EU/EEA citizen has a UK Residence Certificate, in that less questions will need to be answered on the application form.