I have a 5 ft wide sled that has a replaceable insert like that.

One problem I ran into is that the wood on either side of the insert sits higher then the insert due to the glue between the first and second layers of plywood  

It’s not much but it leads to some less then perfect joints.  

I’m going to make another one and use 3/4” wood for the base but I’m going to pocket out where the insert needs to go to fit the 1/4” birch I use for my laser cutter to make it perfectly flush and cheaper and easier to make replacements.