Its already the case.
You get increased rewards for more portals finished, max rewards for all 4 portals with a guranteed reroll shard and a Rotom.
Your suggested numbers are too high, keep in mind that the dungeon can be finished in around 15 minutes daily if you take a full party of players. You are also able to collect more glitter if you put effort into beating the trials with which you purchase additonal daily entries to the dungeon.
Rotom is already a guranteed reward for 4 portals beaten. Bagon is also a potential reward. The others wouldnt make sense for the dungeons lore. In other dungeons you are able to have other pokemon as rewards.
You are already able to synch your pokemon with the Pocket Natu augment you can purchase with Glitter, even with an unusual increased chance.