This is an idea to add even more diversity and (imo) fun to Invention Sets. Is it too powerful? Maybe, but I'll throw it out there and see if there's any interest.
A new Wildcard IO would not give any direct enhancements, but would count towards the Invention Set Bonuses of every other IO slotted into the power.
Example: if you have one "Thunderstrike" IO and one "Devastation" IO slotted in an attack, you get no Set Bonuses. But add a Wildcard IO, it counts towards BOTH and now you get the first bonus for both sets. The trade-off is that the Wildcard itself is a wasted slot, it doesn't enhance the power at all.
Only one Wildcard IO allowed per power, so you can't get two fourth-tier bonuses. I'm not even sure how often people would use them, this idea is just a fun option to add to creating builds.