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 +136,24 @@ 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 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.
+
+ * 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 using descriptor wallets (BIP-0380)
+   in addition to a seed however.
+
+The [SLIP-0039](https://github.com/satoshilabs/slips/blob/master/slip-0039.md)
+scheme addresses the wordlist dependency issue by standardizing on a
+single wordlist.
+
 ==Reference Implementation==
 
 Reference implementation including wordlists is available from