I know turbine has already said there will be no new traditional instances or raids with Helm's Deep, but there are a few things I'd like to see with the ones they scale and the ones they plan to make in the future..
1. LOCKS. Locks are your friend (even if it doesn't seem like it at times). Locks are a very good method of preventing farming (and when an instance is farmed too often, it quickly becomes boring/less fun. And bored players are unsatisfied customers). Even just a limit of doing the challenge on a 3/6 man once per day would help. A 1-2 day lock on the Erebor raids would have easily prevented the mass farming that occurred. Also, when scaling, don't break up the raid (i.e. Ost Dunhoth). That promotes farming of the easiest wing (not that anyone really does OD when they could simply do NCF or STH and hope for some golds). A t2c raid should have locks, and a player shouldn't be able to do it as many times as they want in one week's time.
2. Some kind of barter system. Erebor Gems was okay, but since the gems were tradable and you only needed 9 to get both rings and your necklace, there was no point in continuing to do the raids after you had acquired all the ones you need (besides a FA symbol, but we all know it wasn't long before everyone had at least one of those). Turbine did well in the past with special drops from certain bosses that could be turned in for gear (i.e. Rift, Watcher, DN, OD) and with other prizes per boss chest, such as Moria/Lothlorien medallions, Orthanc sigil fragments, etc. which could be traded for jewellery and gear.
3. Loot. This one is closely connected with suggestion #2. When you do the current 3/6/12 mans, its quite discouraging to open the chest at the end and mostly find bounties and relics. That just makes it seem like doing the instance was a waste of your time. This is where the barter system comes in. Putting SOMETHING in the chest that's worthwhile makes the disappointment not as great, and inspires the desire to want to do the instance again. I recently did a BG t2c at 85, and the only thing I got out of all 4 chests was a Tarnished Symbol of Celebrimbor (which I had no use for), and some bounties and relics. I think it's wrong that one should feel like they came out of a t2c with nothing but relics and bounties. Also, don't make teal items trade-able. That is just another way to defeat the purpose of doing instances/raids, when you can just go to the AH and buy some nice teal jewellery/gear.
4. MULTI-BOSS RAIDS. This has more to do with future instances, since Turbine has scaled some multi-boss raids. But they are simply more fun than single-boss raids. With single-boss raids, you just go in, kill the boss (or trolls, or easterlings) and you're done. With multi-boss raids, you've got to clear trash along with 3+ bosses at least. It takes more time and thought, which to me (and I'm sure most raiders) is much more fun.
So please Turbine, if you still care for the raiding community even a little, help us. Give us SOMETHING to work with. Please.