The trial dummies were a really good addition to the game. The buffs they provide might not be 100% representative of buffs in a real group, but they provide a great standard training tool for all classes. Using one has certainly helped me be a much more effective DD.
The problem is, to make the most of it you have to burn through expensive potions. I don't mind using some but I'd rather save them for actual content, so it limits the amount of parsing I can do, as I don't have hundreds of thousands of gold to burn on spell power potions or flowers. The situation must be even worse for newer players in the game who have even less gold. So we have this amazing training tool but it's made quite difficult to make the most of it, you have to choose between using your good potions for content or for training.
This is only really a console problem - on PC I think you can just copy your character to PTS and parse away to your heart's content with essentially free potions. But it is a real problem, and at least on console it makes the learning curve for new players that much harder.
So here's my suggestion:
Introduce training potions (and poisons too, I guess). These would be craftable in exactly the usual way at a crafting station, using exactly the same ingredients as the real potion you want to replicate, but with the addition of an animus stone. Training potions would only be usable on training dummies, but would not be consumed on use. Only 2 checks would be required: 1) are you in a player house? (That's the only location training dummies can be found) and 2) are you in combat with another player? If so, the potion doesn't apply.
Animus stones are already used in the construction of training dummies, so using them to produce training potions is consistent. It requires only the introduction of the new training variants of potions and a minor UI change to alchemy stations. It would be a boon to master crafters, as animus stones are available for writ vouchers so there would be another opportunity for crafters to make training potions and sell them to other players. And there's an opportunity for ZoS too, as they could also sell bound training potions through the crown store.
I would happily spend my writ vouchers, or even crowns, to buy a training spellpower potion for use on the dummy in the knowledge that I could parse away for as long as I needed without worrying about wasting valuable real potions. There wouldn't be any real downside as the market for real potions would still exist for people to use in real content, but it would help new players (and old players trying a new class) get to grips much more effectively with their character, increasing player enjoyment and retention.