Here are several suggestions ranging from “could be implemented immediately” to “completely brand new feature”. Some of these are similar to other options already suggested.
Suggestion A - Solve the useless token problem. Either make 1* characters champable and farmable, or filter all standard tokens to elite tokens at a certain Shield Rank. This means all tokens are either building roster or feeding champ rewards. There is still a steady stream of 1* covers available in PVP if any advanced players really want them in 3* land or higher.
Suggestion B - Every 4* and 5* character gets a feeder as soon as they hit the tokens. For this, some 3* will have to feed multiple characters. This will require replacing some of the LTs in rewards with 4* covers. While this may seem on the surface like a raw deal for players in 5 * land, remember that more guaranteed 4* covers equals more guaranteed 5* covers from feeders. Make all feeder information readily available through an in-game official source. The increased number of rewards changes as characters are added are sure to upset some players who may have just missed a milestone rewards. To accommodate this, add a reset option for champion characters, much like resetting a vault. Make it cost 1k HP, same as a roster slot, and the character goes back to base champ level so you can earn all champ levels again. The sell option will still be available so there is an interesting opportunity cost between flipping for iso and HP payouts vs paying to reset to base level to start the rewards again a little quicker.
Suggestion C - New weekly ”Collector " store. Picture a cool store page featuring Taneleer Tivan, with a few of the featured characters in the background in giant experiment tubes and containment chambers. The list of available characters would update weekly to include: this week’s boosted list (all tiers), all required characters for this week’s PVE, all featured characters for this week’s PVPs; so a relatively short list. The store would have 2 tokens available to buy, a “Collector Heroic Token” and a “Collector Legendary Token”. These would have the exact same prices and odds as regular Heroics and LTs, just a much narrower character pool. This benefits both new and veteran players, as extended access to weekly boosted and featured characters allows all players to build their rosters for immediate success in current events in all tiers 2* - 5*, while the narrower character pool would allow veteran players to spend their HP and CP to increase odds for needed characters in the diluted wasteland of ever growing 4s and 5s. Mix a couple of these tokens into progression and placement rewards and you’ve got yourself a winner. Run a special Collector event featuring these tokens. The possibilities are endless.
Suggestion D - Bonus Hero Vault. Each week, a special vault is generated using only a player’s individual bonus hero favorites. Contains only 10 covers: one 5* (10% chance is slightly lower than a standard LT, but it’s a guaranteed favorite), two 4* (20% chance is a good bit higher than Heroic tokens but 4* is the worst diluted tier), and seven 3*. Tokens cannot be purchased in any way and the vault cannot be reset. Tokens to this vault can only be earned in 3 ways. First, as a bonus reward for those who make in game purchases. The odds of pulling a “bonus hero vault token” from a bonus reward would be equal to the 100 HP reward so relatively rare. Second way to earn would be a new reward tied into daily resupply for collecting 7 days in a row. Third way would be a couple mixed into VIP rewards. Tokens to this vault cannot be hoarded and if there are any unused tokens when the vault flips, they auto pull similar to how covers auto sell at expiration. This rewards loyal players and spenders with an extremely limited token with a completely controllable and small character pool. Players can guarantee 1 pull a week with 7 straight days of play, guarantee maybe 1 more a week by buying VIP, and have a very rare chance at maybe a couple more by spending to activate a month of bonus rewards. And because it’s non-buyable, non-resetable, and non-hoardable,… It’s a nice perk that would be pretty much unexploitable. In the nigh impossible situation that a player would receive more than 10 tokens in a single week, the game can substitute any overage tokens as LTs.