I think it would be nice to see a new Pet Vendor added to the pet pavilion or the shopping district that allows players to "trade in" their pet for a specific pet related currency instead of gold and instead of trashing.
The concept of "trashing" a pet seems wrong, and "quick selling" pets is also, so maybe players could give up pets for "adoption" in return for pet training related item (elixirs) or currency (like hatching peppers). This could scale based on the pedigree of the pet, or how old the pet is. So, the more trained a pet is the more of a return players will receive. This way, players could turn their "failed" pets into something useful, and the negative of failing a pet would have a positive turnaround for players instead of being an instant demotivator.
This idea could also be expanded by letting other players spend large amounts of gold to "adopt" a pet from the vendor. It would be a mini-bazaar for pets. This would let other players use a partially trained "failed" pet that isn't wanted by other players as their own starter pet, or just let newer players who aren't interested in training their own pet adopt one. If this system would still be too easy, it could be gated behind a player's leveling progress in the game, or through specific pet training related badges, like having trained X number of pets, or mastering every pet game. It could also be gated behind the player having, for example, at least a Mega level pet to adopt an Epic level pet (one level down). This system could also exclude no crowns and no hatchmaking pets for obvious reasons, and could extend to even more pets on a pet-by-pet exclusion level. After a period of time, pets could be quietly "removed" from the pet vendor and sent to a "red barn farm" if they're not adopted by another player.
I think this would pave the way towards adding additional ages / level ups to pets, so they can be trained for longer. Because having a system in place that minimized the pain of "failing" a pet and rewards players for getting farther along in their pet training was one of the reasons pet training hasn't been able to be expanded in a long time.
This would also let players pick up in the middle of a stage training a pet with maybe less than ideal stats for some players, but perfectly acceptable stats for others. Like if one player was going for all damage talents and got a crit talent, they might normally trash their pet and try again, but to a different player that pet might be ideal for them, and so they could adopt it for a large amount of gold and use it as their starting pet for their own hatching, rewarding both players and making the pet training system continually rewarding.
This also gives a reason for higher level wizards to train pets after they have already "mastered" pet training. They could continue to dump resources into training pets players *do* want and putting them up for adoption.
In summary:
Add a new pet vendor to the pet pavilion that specializes in "adopting" pets in a friendlier Bazaar-like experience instead of "trashing" or "selling" pets
Add a new currency, or use an existing one in place of gold for "adopting" a pet
Reward players for "adopting" their pet based on how trained it is, mitigating the impact of failing a pet
Expand the tiers of pet training to let players train more powerful pets.
Let players earn badges for their pet training progress
An additional idea I'd like to tack onto the end here, it would be great if mastering a pet game gave players more experience each time they played the game. Currently, it doesn't matter how much a player plays a game, players will reach the first tier of the game and then usually choose to skip and spend energy instead of playing a game outright. I think it would be worth it to incentivize players to master a game for even longer, giving them an actual reason to rank up, by making the amount of XP per game go up as players master it. Each level could add 2 XP, maxing out at +8 for a perfect game at the highest level of mastery, the exact amount members get with double pet xp.
I agree wholeheartedly. It definitely feels strange to "trash" pets, and the suggested reworks could definitely add a lot more interest to pet training.