If someone has already done this comparison (transducers vs speakers), I would be curious to know the results.

It's more correct to say Flat-Panel vs. Point-Source speakers because both types of speakers use transducers. You could rip the transducer out of your point-source speakers, press it up against a soundboard and you've got a flat-panel speaker. In addition, the wooden bridge in a piano is a transducer for the strings, so technically, acoustic pianos have always had a transducer.

What you seem to say makes sense, but I think the only way to find out is to compare.
If someone has already done this comparison (transducers vs speakers), I would be curious to know the results.

... The startlingly-authentic grand piano sound is thanks not to out-dated sampling techniques, but to the physical modelling approach of piano sound ‘Guru’ Philippe Guillaume and his firm Modartt/pianoteq.

I am a bit doubtful though about the sound of pianoteq played through a transducer on the soundboard. Don't we hear a modeled soundboard with its proper modes played back on the physical one, not a linear device for sure? Unless there is a special version where the soundboard response is absent from the model, or is properly equalized, I still think pianoteq sounds much better on normal speakers or headphones, (in my opinion of course)...

Of course, only pianoteq can be so powerful with microtuning in real time...

https://www.youtube.com/watch?v=YQuq3iet9zA

I wonder if it’s possible to build a little grand piano specifically for Pianoteq (with a real soundboard, without the strings ...) using transducers to spread the sound?

I think nothing could make Pianoteq more realistic for those who don’t need a '' real '' acoustic grand piano ...