Concealed flush tank for floor-standing WC

I live in a single-family house from the 1950s. In the bathroom there is a floor-mounted toilet with an exposed flush tank. We are considering replacing the flush tank with a concealed solution in a boxed-in extension. Our plumber has looked at it and says that this would not be possible with a floor-mounted toilet, it would have to be replaced by a wall-hung toilet. The costs for that are of course considerable. Therefore my question: Is it really not possible, and if so, why not?

If you google it, you will also find concealed solutions for floor-mounted toilets. (we had that in the last apartment too) The problem for you will be that your boxing comes about 15-20cm forward. Then, of course, the toilet will no longer fit on the drain hole. With this, you will have to change something one way or another, which will then make it sensible for you to use the drain of the concealed solution and a wall-hung toilet.

So, if you already

--replace the flush tank with a concealed solution in a boxed-in pre-wall construction. Our sanitary---

then it makes sense to include the wall-hung toilet in the installation. A room with a floor-standing toilet is harder to clean and simply no longer state of the art! The financial additional effort is limited, the frustration about the missed toilet change lasts forever!

In other words: it is also possible with a floor-mounted toilet. "Obvious" and "state of the art" are not exclusion criteria. It really comes down to a matter of opinion. The frustration with the floor-mounted toilet is kept to a minimum for us (in other words: it does not exist), but with a tight budget, replacing the toilet bowl including modification of the entire drainage system does carry weight. This is about a single measure and not a part of a major renovation.

The change of the drain you have anyway. Whether it is routed forward to the toilet or backward behind the casing probably does not make much difference. Your saving measure would therefore be not replacing the ceramic and that costs about 50€ for a simple one. If that is too much for you, why should any change be made at all?

So far, I had the layman’s view that the outlet of the concealed cistern is simply connected to the toilet connection. There is enough space, and if a few centimeters of pipe stick out of the casing, it’s not a big deal. If the drain has to be changed anyway, it really doesn't matter. But I still don’t understand why it has to be that way and why the toilet can’t just stay as it is.