Please elaborate on what these "obvious reasons" may be; as I am missing them for some reason. Allowing players to play updated monsters as races wouldn't be a problem like letting them play monsters straight from the MM might be. Take Yuan-ti for an example. You could do something like...
[sblock=Yuan-ti]+2 Intelligence, +2 Strength or +2 Dexterity
Medium
7 squares
Low-light vision
Common, Draconic
+2 Arcana, +2 Acrobatics
Poison Resistance: You have resist poison 5 + one-half your level.
Slither: When making skill checks, you can move at your full speed without suffering penalties.
Prehensile Tail: Choose the crushing coils or cobra shift power.
Crushing Coils Yuan-ti racial power
You whip your tail out and grab an enemy.
Encounter
Standard Action Melee 1
Target: One creature
Attack: Strength +2 or Dexterity +2 vs. Reflex
Hit: 1d6 + Strength or Dexterity modifier damage, and the target is grabbed. You get a +2 bonus to resist the target's escape.
Level 11: Strength +4 or Dexterity +4, and you get a +3 bonus to resist the target's escape.
Level 21: Strength +6 or Dexterity +6, 2d6 + Strength or Dexterity modifier damage, and you get a +4 bonus to resist the target's escape.
Cobra Shift Yuan-ti racial power
You flex powerful muscles in your tail and quickly move out of the way of danger.
Encounter
Immediate Interrupt Personal
Trigger: A creature hits you with an attack
Effect: You get a +4 bonus to defenses against the attack. If the attack misses you, you can shift 1 square as a free action.[/sblock][sblock=Ogre]+2 Strength, +2 Constitution or +2 Wisdom
Medium
6 squares
Normal vision
Common, Giant
+2 Athletics, +2 Intimidate
Powerful Throw: You can use your Strength when making a basic attack with any thrown weapon. You also get a +2 proficiency bonus to attacks with improvised thrown weapons, and such weapons deal 1d6 + Strength modifier damage on a hit.
Brawler: Make improvised attacks (including unarmed attacks) as if you were armed with a club.
Large Combatant: You have the large combatant power.
Large Combatant Ogre Racial Power
You are smaller than your savage cousins, but still large enough that it counts.
Encounter
Free Action Personal
Effect: Increase the melee reach or range of your next attack by 1, or begin a burst or blast from any adjacent square.[/sblock]