I am with you on this one.
I mean yeah... arguments like "Too confusing for new people". Come on, the separated eco is already confusing, towny commands are confusing, stuff is confusing for kids.
"It will become a normal thing to have custom ranks". Whatever really. You paid for it, enjoy your custom title.
You could have 2 types of custom titles. One given out as an honor with one color and the other one bought - with a different color. Done.
If you put a hefty price tag on custom titles, we'll all be just fine. I would consider buying a title.
Suggestion: if custom titles become a thing, it would be nice to have a 'custom rank': X and 'donator rank': Y in /seen.