I recently saw a video discussing the Japanese ring growing system. You use the standard mesh wire fencing, and form it into a tall cylinder. You stake this down with tall stakes, and then fill the bottom with compost. The tomatoes are then planted around the outside of this mesh fencing system. It's claimed that they then feed off of the compost from inside of this ring. Here is the video that I watched which describes this system:
Now, I ponder the question if it's possible to combine this ring growing system and hugelkultur. They didn't use much compost in the video, but I propose that one could build a larger hugel base, and then cover that with a good bit of compost. I would imagine that it would be best to use wood that you have already had going through the compost process, but that this need is lessened with the higher amount of compost that you put on the top of it. Of course, I would layer the wood and compost to create a firmer hugel bed, and then I would cover with a nice layer of just compost. I also would consider planting the inside of the ring with some short legumes or other nitrogen fixing plants, to help give the tomatoes everything that they need to grow.
I guess this could turn into a form of three sisters planting with hugelkultur in a Japanese ring. In this video, he talks about using kitchen scraps and making this japanese ring an active compost bed. Personally, I would want to add my already composted material for the best results.
The usual method is to create a keyhole garden space with the compost stack in the center of the raised keyhole bed (the keyhole gives you easy access to the stack).
In this type of raised bed you can indeed use hugel method under your soil seed bed, the compost stack continues to receive inputs and the plants derive many nutrients from the composting in place system.
To make this setup even better, inoculate your seeds/ plant roots with mycorrhizae and use some compost in the soil makeup as you are filling over the decomposing wood in the keyhole bed.
For the soil you can also add wood chips, dry or green leaves, straw to give organic material for the start up and through the years.
This system works so well that several of the TV hosts of gardening shows have featured it at one time or another.
This is a photo of MkII of my composting tower with the MkI in the background.
The MkI is 3ft diameter and 3ft high. It is filled with used coffee grounds mixed with sawdust and composting worms. I grew zucchini in the top very successfully last year and will do it again this year too.
Next spring I will take is apart and use the soil in the garden.
MkII is 4ft diameter and 3.5 ft high, and is being filled with used coffee grounds inoculated with oyster mushroom mycelium.
Based on my experience with this system, I think that your idea is certainly worth investigating further.