Maciej, dCS have already tried marketing a DAC with Phono inputs and RIAA eq. It was part of the first generation of products and was called the Grieg. It was not a success and was quickly withdrawn.
The main problem for committed vinyl enthusiasts (include me) is that in order to function such a product has to digitise the analogue input ( using an ADC) which for many defeats the whole point of a owning a fine turntable and phonostage. It’s like asking a racing yachtsman why he doesn’t get rid of the sail and install an outboard motor 
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