I have Speedplay Zeros from 2012 with the metal cleats and am now riding them with the new Zero Aero Walkable Cleats without problems.
Probably the same is valid for the ultra light action walkable cleats. Speedplay only warns not to mix new and old parts from the cleats (Never install cleats using any combination of new cleat parts and old cleat parts. When replacing cleats, replace all used parts with Walkable Cleat parts.) So I would assume you can use your old pedals with the new cleats from the same series. Maybe contact their support?
I had hoped Wahoo would improve the Website, Documentation and compatibility Matrix faster but nothing seems to have been released to the public since the acquisition in 09/2019. I would also love to buy a powermeter when Covid is hopefully done.
Walking is like day and night. While the old ones were no fun to walk at and a hazard on smooth surfaces like metal and tiles the walk-able ones are really great.
The first cover lasted over 8.200km and the second one now has 6500km under the belt and is still looking good. But the old cleats were worn out by walking quickly too. At least now you can just swap the rubber cover and not swear at the nonexistent thread from the poor rest of the screw head.
Best of luck,