I think they need to lower the cost of curing resplendent shards, as right now they are not being used. It cost 1200 fuel to cured, which is roughly $9. There is rarely a illuvial worth $9, so they are not worth using. Tier 5 illuvials are worth $4.50. Even tier 4, stage 2 illuvials are worth $4.20. You'd have to see a tier 5, stage 2 for it to be worth using. And then your capture rate is not that great.
It also gives you double the capture rate as epic shards, but epic shards only cost 160 fuel or rougly $1.20 right now. To pay 7.5x to only get a double the capturing rate isn't worth it.
Honestly anything you would use a resplendent shard on, you are probably just better off buying on the marketplace. If you use a resplendent shard during a stage 3 run, it would cost you 2550 fuel alone or $19 (1350 to do the run, and 1200 to cure the shard). You could buy most illuvials on the marketplace for that price.
I understand that if you lower the cost, more people will use and that will mean more illuvials being captured, which increases the supply and lower the cost of illuvials on the marketplace. You would need to solve the supply issue another way, but as of right now resplendent shards are broken and no one is going to use them.