BIP-39: Add shortcomings section, drop comments headers.

Author: ajtowns

bip-0039.mediawiki

@@ -6,8 +6,6 @@
            Pavol Rusnak <stick@satoshilabs.com>
            Aaron Voisine <voisine@gmail.com>
            Sean Bowe <ewillbefull@gmail.com>
-  Comments-Summary: Unanimously Discourage for implementation
-  Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0039
   Status: Deployed
   Type: Specification
   Assigned: 2013-09-10
@@ -138,6 +136,35 @@ Also see https://github.com/bip32JP/bip32JP.github.io/blob/master/test_JP_BIP39.
 
 (Japanese wordlist test with heavily normalized symbols as passphrase)
 
+==Shortcomings==
+
+Some shortcomings have been identified with this proposal:
+
+* Generated seed depends on the wordlist that was used for the
+  mnemonic. Because the "mnemonic to seed" process uses the mnemonic
+  sentence directly rather than the original entropy, translating
+  the mnemonic to a different wordlist necessary creates a completely
+  different seed.  This is not an issue if you only support the English
+  wordlist, as recommended above.
+
+* Because the seed is generated by hashing the mnemonic, it is not
+  possible to represent an arbitrary BIP-0032 seed via a BIP-0039
+  sentence: the conversion is one-way only (from BIP-0039 sentence to
+  BIP-0032 seed).
+
+* The checksum is short. This means it only gives modest odds of catching
+  random errors (1-in-256 errors will be missed). It is also not able
+  to provide any assistance in correcting errors.
+
+* No versioning scheme. When originally introduced, there was no way to
+  distinguish the address format that should be used for a BIP-0039 key.
+  This is now largely mitigated by use of descriptor wallets (BIP-0380)
+  in addition to a seed however.
+
+New deployments should consider using the
+[https://github.com/satoshilabs/slips/blob/master/slip-0039.md SLIP-0039]
+scheme instead.
+
 ==Reference Implementation==
 
 Reference implementation including wordlists is available from