Technically the reputation tabards are already in the TBC content, but they require EXALTED reputation to attain. Which kind of defeats the purpose of getting them in the first place.

Solution: Reduce the requirement to FRIENDLY, and make it possible to "Champion the cause of .... faction" just like the Home cities (vanilla dungeons) and WotLK/Cata dungeons.

@Darkthunder

The BC tabards were your reward for getting to exalted, hence there is no purpose being defeated. You automatically get reputation based on what BC instance you're running.

It isn't likely to change any time soon, since Burning Crusade instances are hardcoded to give rep to certain factions. Northrend instances were designed to give rep to a default one if no tabard were worn, but Burning Crusade instances gave it to specific ones. This won't allow the tabards to work. Blizzard already said they have problems changing them right now. So it will probably be another content patch before that gets changed.

Sorry to disagree, but for myself I really hope they will keep the exalted tabards and the couple dungeons for rep thing.

Why? Having thrallmar, sha'tar etc tabard should "mean something".
Also iirc BC tabards are last of the old type of "exalted to get".
If every tabard would be given by mere friendly stuff like 30 tabards achi (that comes in 4.1) doesnt seem to mean anything at all, just get 30 reps to friendly and get some honor for pvp tabards (not AB rep tho)..thats couple quests for every faction really while levelling (it should be sort of same way as 40 exalted IMO but less still slightly grindy).
I know it can be pain in the ass to get rep for those BC factions but what else would you grind them for if not tabards?
Surely you are not using epics they give out, since you are going to northend. You wont be using those head/enchant resistance enchants. Nor the pvp set of blues - most likely.
Therefore its tabards that, atleast me, will go for when I did BC to exalted couple months back so I can use different colors that fits the gear I use.