Right, so I am not aware if you are familiar with the way the being "3CX Supported works" but I will explain if you are not.
It only means that 3CX Support will not offer you advise if something falls into the "Un-supported" bracket. Most things that "talk" SIP can integrate with 3CX and I do know of people with peripheral products (such as media Gateways) who configure them manually - IP phones not so much.
So in short - manual configuration and multiple accounts will work, 3CX will simply not advise - but thats what you have the forums for.
I would agree however it would be nice to understand why they don't support multi-accounts, I would assume its because they would have to re-write and add more templates - it can be a time consuming endeavor.