Explain why Stake Program wasn't used

Author: Tyera Eulberg

proposals/0106-paritioned-epoch-rewards-pda.md

@@ -75,9 +75,16 @@ struct PartitionData {
 The address of this PDA will use some bytes -- to prevent griefing and namespace
 the PDAs -- and the rewards distribution epoch number as a little-endian u64 as
 seeds. Specifically: `[b"EpochRewards",b"PartitionData", &epoch.to_le_bytes()]`.
-The owning program should be the sysvar program id:
+The owning program should be the Sysvar program id:
 `Sysvar1111111111111111111111111111111111111`.
 
+Ownership by the Stake program was also considered, but would require either
+extending the Stake state enum definitions or for parsers to do special handling
+based on data length. Meanwhile, this PDA has more in common with existing
+Sysvar-owned accounts: like other sysvars, it is written and controlled only by
+the runtime. The only difference from a traditional sysvar is the
+program-derived instead of a static address.
+
 ## Impact
 
 The change in this proposal does increase the number of "forever" accounts that