Sure, but the new .25 slugs will become better than the old .30 cal. The .22 slug only outperforms the old .25 pellet, not the new .25 slug. You can buy swagged slugs for virtually every caliber sans .177. (at least I don't think there are .17 slugs) NSA, Venturi, MrHollowPoint, etc., all make great slugs for all capable calibers. You can even buy Hornady black powder ammo and use those in the air rifles. I shoot Hornady .50 cal ball ammo meant for muzzle loaders, as well as Hornady slugs (385 grain .50 cal Great Plains). They are NASTY.
The next evolution in the airgun universe will be in ammuniton, and that will give us a considerable bump in efficacy and BC. Better hunting rounds will be developed and manufactures of air rifles will take notice as well all want to shoot something besides a big metal dome with an umbrella attached to it. It's a wonder the damn things even fly the way they do. The new ammo coupled with the better tuning and power per shot that guns are getting out of the box is going to push air rifles into the mainstream more than they already are at the present. It will be up to us to keep the soccer moms and blissninny gun haters away from our freedoms. We will need to be loud and not give an inch to them, ever. Remember that they cannot legislate away a gun that you already own, as there are no ex post facto laws in the USA. However, we all need to get ready for the inevitable Democratic handwringing that will be inflicted upon us all should the liberals find out we are having any fun and not bothering anyone. I am already waiting for the Brady Bunch to have a "Don't Shoot Your Eye Out!" peace rally at the capitol.