I'll start with the why, and then move to what Bretonnia needs.
Bretonnia has received no new unit types after it's release (only RoR), and the old world update for Bretonnia just moved some buildings around and added more work in managing the pledges. If we take a look at lord, hero, and unit types we can see a clear pattern of under representation for the faction. I understand that the official books for Bretonnia were rather slim, but CA has often had some creative freedom for adding units to factions. (I will not look at Chaos or Beastmen at these comparisons. Chaos is the focus of game 3, and Beastmen the most likely candidate for next lord pack)
Legendary Lords: 4, this is a decent number, I would be happy with a unit pack, but that is not a DLC type we have seen for WH2.
Lord Types: 2 (Lord, Prophetess), Second lowest in the game (tied with Dwarves, Norsca has only 1), with only 2 different lord types, which offer no differentiating bonuses to units, there is little to encourage variety in army composition.
Hero Types: 2 (Paladin, Damsel), Lowest in the game, Bretonnia is missing key hero actions and hero variety due to the low number of heroes available. Most notable, for me, is the missing 'Block Army'. Ambushing is un-chivalric so Bretonnia has little to combat the runaround armies.
Unit types: 24, lowest in game, a normal lord pack adds around 4 new units which would do nicely to spruce up the roster.
Regiments of Renown: 6, the bare minimum, getting RoR variants of new units would improve the amount and variety in Ror for Bretonnia
What I want to see updated for Bretonnia:
GREEN KNIGHT SHOULD BE A LEGENDARY HERO!
Rather self explanatory, a simple quest line for acquisition of the Green Knight for all Bretonnian factions. He could also just be an added reward for the players legendary item quest line (like Throt has Ghoritch). And do give him a skill tree, he feels so barebones right now.
Bretonnia needs a fun mechanic to balance all the work mechanics.
Now that Bretonnia no longer has the green knight button (see above) all their racial mechanics require upkeep and management, and most of this is just to have basic functionality like income. Manage peasants or tank you farm income, don't flee or lose the only positive racial mechanic you have, don't ambush or sack settlements if you want to keep advancing in the game, all this is work for the player. I have toyed around with what might be added in place of the green knight button and I think a Grail Hunt mechanic would fit the style of Bretonnia very well. It could be activated once per chivalry stage and with a cool down after reaching max chivalry. (If anyone is interested in what I thought up for the mechanic I'll make a separate post for it. It's even really easy to implement, but since it sidesteps the topic a little I won't go into it here.)
Low numbers in all unit areas makes Bretonnia have little variety. A simple paid for lord pack inclusion would go a long way in offering variety for Bretonnian players. If you add in a few fun improvements, Bretonnia would be elevated to a new level of play.
If Norsca is not updated with WH3 a Bretonnia vs. Norsca lord pack would be quite nice to see.
Which factions do you feel most need an update? Is the mighty Bretonnia included in your list?
Quick Edit. Please correct my numbers if they are wrong, I'm at work and just used a wiki entry to check them.