I've played two bass drums since 1968. If you wanted double kick, you had to have two bass drums, as there were no double pedals around. I also used the Ludwig
Speed King pedals for years until the footboards disinegrated. If they redesigned that pedal using a wide platform, it would be bulletproof. I never had to replace a spring as the springs (one on each side), are compressed, not pulled - best spring/cam design ever in a pedal.
Trixon made their bass drums oval in shape with a flat bottom, that would accomodate two pedals side by side and since the drum looked squashed on one side ( shorter on one side), one would get two definite tones using both pedals. Replacing heads would be killer, since Trixon was the only game in town when it came to those odd shaped heads. I do not think they are in business anymore...they went the way of Studebaker, and rightly so.
Another thing is hitting both kicks at exactly the same time is something you cannot do with double pedals...try it and you will find out why. Why hit both kicks at the same time? Because its huge, thats why. Kick flams have their place too. nuff.