'x-' prefix on charset names

Hello, 

I have a question regarding the 'x-' convention used to 
indicate that a charset is not registered at the IANA registry. 
Is it prohibited to use a unregistered charset at one's own risk? 

According to the latest CharMod paper, the convention is 
discouraged as follows (Excerpt from Section 3.6.2): 

  [S] The 'x-' convention for unregistered character encoding 
  names SHOULD NOT be used, having led to abuse in the past. 
  ('x-' was used for character encodings that were widely used, 
  even long after there was an official registration.)

My question is about the intent of this is. If an unregistered 
charset was used, you will be forced to avoid the convention 
for complience. I think there are good reasons to avoid it, but 
what should be the options to take? 

Among the following viable alternatives that I can think of, I 
understand W3C is in the position of recommending option a and b. 

 a. Use a registered charset instead (May or maynot be feasible)
 b. Get the charset registered (May take time)
 c. Use the unregistered charset (Need bilateral agreement)

It is not clear to me if W3C intend to prohibit option c. Could 
somebody clarify the intent, please? 

I appreciate your attention. 

Thanks,
-Dan
-- 
Dan Chiba
Server Globalization Technologies
Oracle Corporation