Then just do it like flower pots and use red bricks to craft plates directly. This is called the "following how Mojang does it is more important than realism" technique. Try it.
Personally, I'd rather we just have item frames placeable on topsides and undersides of blocks. Then when you want to eat something in there, you right click the item frame that is used to "represent the plate", and then eat the food totally normally. After all, we do not have dedicated chairs blocks, we just use stairs or slabs with maybe signs and doors or trapdoors to make these chairs sidearms and backrests, because really why add not absolutely needed/blocks when stuff that is already there can be slightly patched with a tiny modifcation to do the job just as well ?
With the item frames you'd get not only "food plates" but you'd also get a LOT of functionality for all other players. It would require almost next to no actual coding would be needed, and the uses and possibilites both decoratively and actually useful would be incredibly bigger than merely to just put food on a table. I'd place huge "connecting" maps right on the very roof or floor at the central room at my base, for example.
Also, why would I want the annoyance of having to eat my food one small bite at a time when I can just eat an entire food item in one go ? I'm not that patient of a guy lol so if I want small value food then I eat a small value food, and if I want a big food alue food then I eat a steak or something very sustaining. Making ALL existing food eatable in small chunks would also detract too much from their differences in utility. There would be even LESS of a point making small value food, because you could just eat big value food in steps instead.
Thus, I see no real support for a dedicated "plate" item. Especially one that allows eating food one bite at a time.
Awesome idea! Here's an example of a situation that plates would be great for: You have a bunch of mobs chasing you and your about to run out of enough hunger to run. Put a plate and some steak down and your all good.